So it will certainly take time, and it will take smaller, riskier companies demonstrating that some futuristic new platform is soooo much easier, but if that really was the case, it really wouldn't be that crazy to see large enterprises starting to shift this way.
Of course this is all based on the assumption that "it's going to be so much better and easier to use that it's obvious to the market as a whole." I'm not saying Apple will achieve that goal, but I think a lot of people who wouldn't traditionally have been "Apple fanboys" are rooting for Apple, simply because we've all seen them make transformative changes with the iPod and iPhone, and we like progress.
Sounds like you have never worked in an enterprise. Ease of use for the staff is definitely not at the top of the list of concerns. They care about price, will it continue to run their legacy apps for another 10 years, how easy is it to administer etc.
Regarding your second point, I have not heard anyone who is not firmly an "Apple fanboy" cheering for iOS to supplant Windows in the enterprise. Linux, yes, iOS no.
You're talking about this in theoretical terms like the iPhone isn't already doing very well coupled with Exchange in the enterprise space, but it is...
The iPhone costs enterprises about the same amount as a good Android phone (e.g. Galaxy 4/Note). So it isn't uncommon for companies to offer employees a choice of either an iPhone or Android phone, since both hook into Exchange equally as well and cost the company a similar amount.
Blackberry is dying as the go-to enterprise phone. Has been for a while.
A desktop Windows computer is faster, cheaper and more capabale than any phone out there. Dumb terminals are dramatically cheaper. That's why almost every office worker in the world uses them. iOS is doing well replacing Blackberry and Palm Pilot in the enterprise, not replacing Windows machines.
iPhones already exist in the enterprise space. They aren't going to need to buy more of them to use them as laptops, just keep buying the ones they're already buying and use them for two things instead of one.
It is going to be a lot harder for iPhones to become capable of taking over the job of a Windows PC than for a small Wintel phone to fill in the job of an iPhone.
If convergence devices do appear in the enterprise I think its more likely that the popular ones will be Windows, Android or at an outside chance Ubuntu - and the devices more likely to disappear are the ones not best suited to the desktop work.
First of all, "light browsing, reading, and phone calls"? You clearly haven't been in sales. Entire 2000 word screens are usually banged out on one's iPhone or Blackberry. The calendar app has to manage hundreds of events, etc.
I do almost all of my browsing on an iPhone.
Airline mechanics at at lesat one major global airline have been using them to log their maintenance activities with precise detail.
More than one Class-1 railroad is prototyping iPhones and iPads for crew and yard devices to manage train manifests and marshalling orders.
Doctors are using their iPhones for looking up and editing EHRs in some hospitals.
Everywhere I look in the enterprise, they are killing the PC in favor of the smartphone -- today.
For "real" office work that needs a convergence device, Apple is in even less of a strong position, for the reasons outlined elsewhere.
They are likely to find some niche applications, and probably do well in the consumer side, but its hard to imagine Apple having much success as a PC replacement (and decreasing success in the long run as a BlackBerry replacement)