"Oblivion/Fallout3/NV saves are kind of large - might not work so well with the Cloud. "
Gigabytes large? Not even close.
/facepalm
My FO3 save dir is ~ 30mb, and that's not a lot in there. A quicksave, and maybe 5 saves. Steam gives you like 6mb per game, AFAIK.
Also, VALVE IS NOT CANONICAL. What they give you is completely unrelated to what VALVE does.
Some conjecture:
Ubuntu gets a lot of pro-bono mirroring to lighten load.
Ubuntu's systems are not geared for throughput like a game/media distribution system will be.
VALVE is hosting -metric-buttloads- more data than the Ubuntu mirrors. This I know, because I manage a local mirror. My own collection of games, installed, takes up about as much (or more) space than the entire production Ubuntu mirror. (and you KNOW I don't own close to everything they host)