I asked this in the Podcast Questions thread about an hour ago. Odd coincidence...
But anyway, I don't
think it means anything more than "Bethesda is planning to allow us to make DLC but we don't know the specifics, such as how many DLC packs we can do, quite yet." I doubt Bethesda would develop the DLC themselves as they have two projects they're working on themselves, and I don't think they want to add even more things to their plate. But of course, this is just what I think, who knows what the reality is.
Personally I wouldn't like Bethesda doing it as FO3 wasn't that great and it seems kind of disrespectful of Obsidian if they can't do DLC for their own game.
Regardless of your opinions of the game, keep in mind that if Bethesda never made Fallout 3, Obsidian would never have gotten the opportunity to make New Vegas, let alone DLC. I think Bethesda has every right to tell them what to do with the game if they want to.
That said, I don't like the idea of Obsidian not making their own DLC either but I feel that Bethesda wouldn't do that. At the most Bethesda may choose the locations for them, but I really doubt they wouldn't let Obsidian develop the DLC themselves.