PS3/XB360 level graphics still requires a fair bit of content and the web-game-ecosystem kinda died off with Flash and people moved onto mobile or focused on marketplaces like Steam/XBIndie,etc.

I do think we're due for a new wave of web-based gaming though, web audio just wasn't near maturity when Flash went and the mobile/steam/xbindie marketplaces still worked for indies. But now with all the crowding and algorithm changes people are hurting and I think it might just be a little spark needed for a major shift to occur.