John, Zepto is _exactly_ intended for targeting bleeding-edge WebKit mobile browsers. Doesn't the README clearly state that?
http://gs.statcounter.com/#mobile_browser-ww-monthly-200909-...
It frustrates me to no end that the only JavaScript tools being developed in this day and age, for mobile platforms, exclusively target the latest WebKit: Sencha Touch, jQTouch, Zepto, etc - they all exclusively focus on the latest WebKits and it's completely baffling. No web developer in their right mind would drop support for IE - no one would hire them - and yet they seem to be fine taking that approach on mobile.
Even if these tools are only being built to be used within a "safe" environment like PhoneGap - web developers don't understand that distinction. If the only tools for mobile web developers target WebKit platforms then web developers will only ever target WebKit platforms. As has been shown in the past competition is absolutely critical to the health and longevity of the browser - when one platform dominates and doesn't receive competition the platform will stagnate.
Not only is targeting multiple platforms pragmatic, you get more users visiting your sites thus making you more money, but you also help the health of the mobile web as a whole: Pushing more browsers to compete better and provide an improved experience to all users.
I don't want to be restricted by implementing something what works on every mobile browser (do you still support WAP?). Again, I want to build the most amazing applications. If that means some browsers can't show it, well, too bad.
I'm doing the web a disservice because I release a library that only works with one mobile browser? The web as a whole will suffer from that? What do you know about my customers? What do you know about the sites and apps I want to create?
And web developers aren't smart enough to understand the difference between developing for PhoneGap and the web?
Please don't lecture me about making money and about making awesome user experiences. I can very well take care of that myself, thank you.
Right now it makes a lot of sense to only target WebKit browsers simply because it's the only decent rendering engine that's available on decent mobile phones. Zepto could easily support a mobile version of Firefox or IE once Firefox catches up in terms of performance and size and IE catches up in terms of support for HTML5, CSS3 and other emerging web standards.
Finally, stating that "web developers don't understand that distinction" sounds slightly derogatory, don't you think?
Companies like making money (naturally). iOS provides a clear path for them: They build an app, it goes on the app store, out to millions of people, and the money comes in. That is undisputed - you can absolutely make a nice living targeting exclusively iOS devices (by extension, WebKit-only platforms).
However this is conflating the problem space of "building mobile web applications" with "building mobile apps that use web tech". Buiding web-tech mobile apps is, functionality-wise, a sub-set of building mobile web applications. Any functionality that you would need to build a mobile web app you would also need to build a mobile app (albeit you can skim far more off the file size and functionality by targeting just apps - as Zepto has done).
jQuery is targeted at supporting "building web applications" and "building mobile web applications" - the two harder problems in the space. When you compare Zepto (designed to make it easy to build mobile apps targeted at a single platform) to jQuery (designed to make it easy to build mobile web applications targeted at many platforms) the difference is night and day.
This is the disingenuous part of this discussion: Zepto is, apparently, exclusively positioning itself against jQuery - even though they are completely dissimilar. However to the lay user that distinction is completely muddled when the API of one is directly compared to the other - when, in fact, they are nothing alike.
A better comparison would be comparing Zepto to XUI: http://xuijs.com/ XUI also targets the best-of-breed mobile platforms and makes it easy to build mobile apps.
I have to say though John that your view of what makes a great app framework doesn't necessarily matter to everyone. I think your philosophy is executed quite well in jQuery Mobile, but that doesn't make your approach the best one for all cases.
Your choice to go for broad support actually weakens the showing of jQuery Mobile on more shiny devices compared to products which have them in mind to begin with. Does that make jQuery Mobile then inferior? Hell no! It's great, does what you set out to do, and does it well.
Thomas' pretty obvious use of the jQuery name to get some attention aside, there's nothing wrong with zepto's philosophy. It differs from yours, but it will undoubtedly have an appeal to some people or for certain projects, just probably not the same projects where someone would find jQuery Mobile appealing.
No consumer in their right mind would use IE on a mobile :/
FWIW my webapp is 20% Chrome, 55% Firefox, 19% IE (All mainly desktop users). So dropping support for IE isn't that insane.
However, everyone here is constantly ignoring Opera. Opera's Presto competes head-on with Webkit in standards support and performance and has higher market share. And Opera Mobile has the best mobile UI in the market (although that's debatable due to personal preferences) and biggest feature set.
What's really a disservice and plan stupid is to outright ignore Opera and even worse not mentioning it entirely when discussing mobile app or mobile web app development.
Mobile devices don't have the staying factor of desktop browsers (most users upgrade their phone/plan every 2-3 years). Shouldn't we target the best devices going forward to ensure that adoption of technology keeps up and everyone is entitled to the best experience overall?