I wouldn't worry. All that's happening is that more and more differening demographics are opening up, allowing for broader and broader types of 'games'.
So yes, we're seeing lots more 'casual' games, and they sell a lot. But we're still seeing lots of hardcore RPG and jRPG, shooters, etc. and they can sell massively as well.
Now like all market changes you'll see some peaks/troughs - so for a while you might feel too many developers are trying to make a quick buck on Wii for example.
But this will settle down. While plenty of developers will focus on quick/casual games you'll still get big hardcore titles too.
As for why they take longer? Well, because they're more complex. Too me the PS3/360 have brought many games to PC levels of detail/complexity for content, etc. and that takes time. However I believe development kits will continue to improve, and as developers get more and more games out for the HD consoles they will increase speed of development.
So I do think you're worrying about nothing to an extent - or at least worrying about something inevitable.
Try to be reasonable... its easier than you think...
