EDIT: Misunderstood Nineaxis's reply
I don't think this has anything to do with Microsoft, the 360 port was done directly by Valve and is being supported by Valve, the PS3 TF2 port was done by EA Games. I really doubt if any of the custom content will make it's way to the PS3 any time soon, if at all. I don't think it's as simple as downloading a file anyways, I imagine something might have to be done to the map files before they would be compatible with the PS3 version.
Don't feel too left out, though. Even though there really is a lot of great custom maps for the PC version, most of them never get played, ever. There's only a handful of servers running a few of the more popular custom maps, and even smaller handful of players playing on these servers. Sadly, the overall TF2 player base haet custom maps. I only wish I was kidding you...