Personally from an ASP.NET perspective, its the same. To me ASP.NET is done. Mixing in server side with client side UI is just wrong, they should be decoupled completely. I want to build a html5/js/css UI. I want to keep it clean and I want to talk to a data service/ or mocked out data service to do what I need. Starting out with ASP.NET, I used to think this is just totally the wrong way to do things! Then ASP.NET MVC came along which was much nicer than all the pain of web forms ( viewstate etc..) , but now as I said already, I want my client side to be written with no knowledge of the server side workings, just plain old html(5)/css and leverage the power of javascript and associated frameworks ( i like knockout.js and amplify.js).

Its the convergence on standards and the sophistication of browsers that really matters. We all use browsers, all the big vendors now are appreciating this, enabling progression to standard presentation technology. Innovative successful businesses are delivering great services and UX using these standards and they are showing the rest that they need to move to keep competing.

Responsiveness and performance are strong drivers for a rich/smart/thick client, there really are very little advantages to a thin client in application terms from a UX point of view.

Managing upgrades is a sinch with browsers, so if you have a sophisticated client side javascript UI its easy to re-release.

All in all, I tend to agree poster here!