Why this site?

Simply put: The Web 2.0 is starting suck. AJAX is great medium but it has its disadvantages.

1. Its bandwidth intensive - Yes, you don't have to load an entire page with AJAX so you gain some bandwidth. But you loose bandwidth and processor cycles if you have to have 100 AJAX queries per session.
2. Searching and Linking is impossible - Try creating a site in AJAX or Flash and get Google to index you, fat chance.
3. Debugging is impossible - Firebug helps but those 'undefined errors' are so indefinite.

Why not Flash?

That sounds good except scripting for it is a pain and you need to load a virtual machine into your already overloaded browser.

Why not Silverlight?

Microsofts' Silverlight looks like a very promising technology.