Yep I saw them on that stage at comic con. They are just the RB2 instruments with a lego look to them. I think they aren't mass producing them because let's be honest would you buy them over the more realistic looking RB2 instruments?
They are absolutely real. I saw them, saw them played and reached under the little tape thingy and touched the guitar. They aren't really made of legos, but are made to look like they are made of legos.
Now that I think about it when the "band" played I was a good deal behind the crowd and only assumed that the lego instruments were being played, so while they looked functional maybe they weren't. Although I don't know why they couldn't be because they look just like RB2 instruments with a faux lego exterior.
I will be so dissapointed if The Lego Group doesn't release Rock Band Lego sets...especially since it would be the first licensed Lego game without actual Lego sets to go along with them. I can imagine a few possible sets...
Beaten Down Van Set
Roadie & Equipment Set
Tour Bus Set
Hotel or Dressing Room Set
There's plenty of ideas they could come up with. At least give us a promo set for preordering!