To develop an application for the web versus the development for an OS, are two different worlds by far. There is not only the technical aspect of filesystems, hardware and low level programming versus the high level web development strategy, it's also the heavily fortified rules of user interface design existing in application development. On the other hand, app developers escape the headaches of making sure their app can run alike in all browsers.
My take on this is to take the best of both sides. UI design guidelines have come a long way on the client side of things. The Apple design manual can by it self carry the entire weight of the user experience. However, the freedom expressed by some web-designers, the ability to throw out old concepts and bring in new ones is something we should have in the mix, as long as these new ideas conform to established truths about what people actually do in front of a screen. Regarding development, I do firmly believe that pure web-developers have a lot to learn from application developers in the fields of efficiency and security.
The problem that still remain, is the speed of the evolution in RIA design. Most people do not have enough computing power to run high end RIA applications. The reason for this is the inefficient browser and the plug in architecture. In a recent interview with Bill Gates and Steve Jobs (yes, together), this question was brought up. Those two disagree on many things, but one thing stood out that they both truly believed in. They argued that in the future the Internet will function more like a giant database, a back end system while the front end part will be handled by client apps running naively on the system of the user. Thereby effectively removing the problem of bad user experience. They make a good point. The thing is, you cannot leap into the future online, cos you can't be sure that people will be able to follow you. And it looks like many developer companies have came to the same realization, just take a look at Air (Apollo), it's Adobes way of moving application development away from the web and onto the desktop, but at the same time keeping the multi platform Flash development environment.
For the future I predict that the web will keep it's role as a place to get information, to advertise and a place to play. But for bigger more complex things I believe that people, given time, will notice the better user experience and the share speed a desktop app can provide. A good example is Apples Google maps client on the iPhone. It's a client running on a phone that actually outperforms the original Google maps client by a factor of ten. As people become more tech capable, they'll demand more, and then we whom are designers and developers should hear their call.. or crash and burn.