I got a quick look before we broke it. Looks promising but one can't help wonder the legality . . .
I believe it's being put up by wizards of the coast. They've been working on it for a while. So I think it's totally legal.
It is Wizards of the Coast and they are selling high quality scans of the old classic books. (So not free.)
It is WoTC's own store, so it fully legal.
Brutally speaking, the fact that it's down speaks to it's authenticity as a WotC site. :) They have had horrible luck with partners for their online apps, such as the character builder and online tabletop.
You're right!
In this case though. the site is run by drivethrurpg / rpgnow, who have been at pdf selling for some time. This should have a decent chance of success.