I can't really get my heart rate consistently aerobic on any exercise equipment. It seems that the most you can hope for (when you're in good aerobic condition) is to tone the specific muscle groups involved in whatever equipment you use.
That's to say - if you use a stationary bike, don't necessarily expect to be a stronger/faster bicyclist as a (direct) result. That's my experience, as a 8-hour per week road cyclist using stationary bikes, anyways.
I was also able to run a 5-minute mile on a treadmill with it set to a 3% grade, got off and wasn't even winded. I'm not a runner, but maybe I should check into it.
Kal.