That's not really true, I think you mean integrated video chipsets. Mobile dedicated video cards, well not comparable to the equivalent desktop version in performance, still use the same drivers at their core. There are separate downloads because mobile devices have so many different device IDs that they require a lot of different .inf files. The drivers are the same and the tech is the same, it's just that they have to adjust voltage, clockspeed, number of cores, etc. in order to get the performance in line for the target laptop. Having said that, every dedicated laptop card from the current gen including the entry level ones exceed the minimum requirements for this game.
I used to own a Gateway laptop with a 9800GTS. Judging by the scores on notebook check for 5650m, it is just a bit behind the 9800GTS. I had a 1920x1200 display but had to run FO3 at 1280x800 using the high settings to maintain 60fps at all time. Didn't mess with settings back then as much as I do now, and didn't know what they meant so I'm sure I could've run it using some variation of ultra and mostly maintain 60fps. I don't see OP's resolution in this thread. For nvidia user's AA was broken in the control panel if you forced it too. Post patch it works again (you could always 'enhance' it but not override) so if the ATI control panel had a setting meant to override the game I'm not sure if it worked or not before and maybe it's working now and performance suffers? Just guesses. For me the game runs even smoother than with the d3d9.dll