The Halo 3 engine is to the Halo 2 engine what the Half-Life engine is to the Quake engine. It is a heavily modified engine not a new one.
http://jumphalo.net/halo3.aspx
"Interestingly, Halo 3 is so advanced in terms of graphics now they call the engine it runs on The Halo 3 Engine, which basically is an updated version of the Halo 2 engine"
The Pitt was updated twice. Broken Steel was smooth sailing unlike the PC (minus an achievement glitch).
That obviously wasn't you because CoD4 on 360 was and has been since release an incredibly smooth experience. I don't know what you're talking about.
Most of the patches they released hardly fixed any bugs. They just added new achievements.
Fallout 3 crashes constantly for a large number of PC users, particularly on Vista. Also, the frame rate in Fallout 3 360 is smooth 95% of the time. Oblivion ran poorly, you are right.
Burnout Paradise's first packs were never paid for. Rainbow Six Vegas' last map pack became free after 2 days after it was mistakingly charged for. And free DLC after some time is still free DLC.
http://marketplace.xbox.com/en-US/games/offers/0ccf0001-0000-4000-8000-000045410830
It is not a patch but a larger marketplace item. It is still free.