No, it's perfectly legal to use the left lane, as long as you occasionally pass people on the middle lane.
Now, as for people doing 280+, I have yet to see one.
You're looking at one. Not very often, but an M3 will get you to 290. There's the occasional supercar as well that I've seen pass me when I was doing 220 or 240.
It's not very often that you have to make way when you're doing over 200, but it happens.
In reality, on sections restricted to 120, you'll have trucks going 90 on the right lane, most people averaging 120-130 on the middle lane, and some doing 150 on the left lane.
True, it's not quite as simple as I made it, but in general, people drive speed limit +10.