Oblivion only reqiures so much GPU horsepower because of the EXTREMELY inefficient render engine. It renders objects even not on view or being blocked by a wall and such.
Yes, I suspect the same with Flight Simulator. It's been the same story since FS2K. A new FS is released, and it basically makes every piece of hardware around look like crap. Many fingers have been pointed to inefficient rendering, because the graphics (while spectacular) shouldn't put THAT much tax on a top-of-the-line GPU.
EDIT: 100 posts W00T. I can see my avatar now