Good questions Contrejour, I initially wondered why they sided with HTML5 but with the fact that Adobe is moving away from Flash on mobile devices at all (Android no longer receives updates, and Linux does not either actually!) I'm very thankful they did.
Aside from easier multi-platform game releases and iOS support, Windows 8's Metro interface is very friendly to HTML5, even allowing the web apps on it's store, so this definitely looks like a platform that will be around for a long time to come now.
As for similar software to Construct 2 I believe there is a free version of The Games Factory 2 which exports to Flash games. The only restriction is that they must be free and can only be uploaded to the Newgrounds portal <img src="smileys/smiley1.gif" border="0" align="middle" /> (They probably have a paid version but it might be like Game Maker where you need to purchase individual exporters).