that's sort of the general consensus, but the actual reason for that is that as woofer size increses, the fs drops.
Also, a properly designed enclosure should be able to do pretty much whatever you want.
One way to think about it, is which would hit low notes better? an 8, or an 18?
So, generalizing that 12's can't hit the lows, and 10's can is pretty much totally inaccurate. I suspect that you think this because you've had the wrong subs in the wrong box.