At best developing exclusively for bleeding-edge platforms is a niche-market. Is there enough interest now to hire a few developers to build HTML 5/CSS 3/etc.-only experiences? Absolutely. Is this a tenable position for anything more than a minor fraction of the web development market? No.
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.