I'm actually with you on this. The Lego demo is pretty cool and it shows what it possible with social/multiplayer built into an app, but it's obviously not something that couldn't be done with native code (naturally, since sockets is a C library/API). WebGL doesn't bring any new inherit 3D tech to the table, on the contrary I've tried to tell people that WebGL isn't even OpenGL, it's OpenGL ES which is a subset of OpenGL really. You can do 'more stuff' with OpenGL or Direct3D proper, period.
What I think makes this interesting though is people are more likely to visit a website than download some software, so the barrier to entry is much lower. That's probably why games like RuneScape are so popular. I've seen people play that game in public libraries, you can't do that with WoW. And WebGL is powerful enough that a lot of very compelling apps can be written in it. Not Crysis (yet?) but definitely stuff at the RuneScape level and much better actually.
With Java and Flash penetration in a decline (especially on mobile, obviously), technologies like WebGL can capture some of that back, and do it in the way that it should have been done to begin with (ie. in the web browser, and as an open standard). It's just a positive trend and I wish Microsoft would be on board with it.