Anyone want to reply to that?
They can build up more hype if they release that sort-of stuff while the game's being announced.
I've seen it happen in videogames, sporting events, new buildings opening, etc.
It's a marketing strategy that people use to get the word out there about an upcoming product. A shirt that says "TES:III Morrowind" would make less money now than it would when Morrowind was first learned about. It lets the sudden and impulsive-buyer fanatics to go crazy and buy stuff.
Maybe it won't even technically be sold until you buy the game, and it'll come in a pack like "Buy this bundle and get a SKYRIM hat too!"
It's also a way for businesses to readily rake a portion of the dough, but early on. It's basically pure PR. Like a trailer for a movie.
P.S. People are more likely to read into detail about something when they see people walking around advertising a product, and that means more potential buyers.