It seems as though Xbox 360 games might soon be able to embed a custom Marketplace within their game - or, at least, that's what a session description for the upcoming XNA Gamefest conference would suggest.
In the description for the session 'A Custom Marketplace? Where Do I Get One!', it says: "Why not use our new and improved 'In-Game Marketplace' to showcase your game's content even better? You too can shine with the best using an extra coat of API, and back-end storage."
XNA Gamefest takes place on July 22nd and 23rd at the Washington State Convention and Trade Center in Seattle, Washington. For more information, check out the event website.