The web is a classic disruptive innovation. It's significantly worse in most measures of performance (speed, ease of programming, consistency) than existing technologies. But it's better in a significant way (ease of deployment), and it lets you do things that old technologies did not (all the social-community stuff). Over time, the performance of both the incumbent technologies and the new disruptive technology increase. However, customers don't need the added performance along the traditional dimensions. When you're already at 30 FPS and photo-realistic images, how much better can you get?
When the web first came out, it wasn't good for much besides documents, and any sort of data-driven form application was very difficult to manage. Now practically everything online has some sort of interactivity. Then people said it would never be able to do office apps - and now we've got Google Docs & Spreadsheets & Presently. Now you're saying it'll never do high-performance 3D games - but somebody has already cloned Doom in Javascript (http://canvex.lazyilluminati.com/83/play.xhtml). Over time, you'll see webapps take over more and more markets from the desktop, until there's nothing left.
(And then the disruptive technology will shift to something else, like cell-phones or neuro-implants or whatever.)