The problem with the Flash runtime and building applications on it is that UI's created on the Flash runtime get very, what's a good word?, sticky?
Look at Balsamiq Mockups. Weird scroll bars (not OS native) and the UI just isn't as smooth as native OS counterparts. Would you want to browse Amazon that was build as a big Flash app? Of course, no one does.
However, it's seems that Adobe has finally found a niche with the Flash runtime, games.
Disclaimer: Since 2001 and 2010 I was a full time Flash platform/Actionscript developer.
