You know I don't necessarily agree with the "it needs WotC or White Wolf to succeed" mentality or the "it's a marketing strategy better suited for comic books not roleplaying games" thing. Here's why.
1. In society(especially American) free is always good. I know people who get free things they wouldn't normally buy or be interested in just because they are free. More than likely any store with a "free" anything sign in its window is going to draw more people just because they are curious or want free stuff.
2. I think that we as people who have already been introduced to games or are knowlegeable about games have a strong dissconnect when it comes to the average person who may have heard of them, or more likely thinks of Final Fantasy and WoW when the term is brought up. I don't think the average person even knows that WotC or hasbro owns Dungeons and Dragons. So how does name recognition really help to draw in new gamers( If they've heard of it and weren't interested enough to check it out, Uhm why would that change?). Now this isn't to say you won't have gamers already in the know stopping by to get free stuff for their favorite game, but how does this increase your market in any way, these people already buy rpg's and supplements.
3.With the less recognized companies it gives them a chance to introduce old gamers to things they might not have been willing to purchase because its not WotC or White Wolf.
If they like it then the company has now gained a new customer, if not then they didn't loose a customer either.
4. Giving someone a quickstart rules pack/pamphlet and running an adventure for them would be ideal. But, as has already been mentioned D&D does this already on D&D day. But that's exactly the point they are pushing their premier game not anybody elses. What about people not interested in fantasy? They could be put off by the fact that this is the only thing being ran. Granted we would still need more than TLG and Goodman Games to sign up so that this issue could be addresed.
5.Note: (This is about the nostalgia comment above) I can't speak for everyone but some people just want a quick game with simple rules and minimum prep time( one of the reasons board games are always popular). Castles and Crusades does this. Is there a nostalgia factor probably, but I game with people who have never been die hard gamers and we played 3.0 and then 3.5 when they came out. Now we play C&C almost exclusively, not for nostalgia but because we can make characters up in about ten minutes, its less reading and memorizing of rules, it starts simple and allows you to add as much or as little as you want(don't really enjoy the inverse of ripping things out to make it simpler). Basically we get to the "fun" quicker and with our full-grown adult lives, responsibilities etc. that is more important to us than fiddly bits and endless options YMMV.