I think what is confusing you is the ability of the motor to move the vehicle in a situation vs. being able to move at the minimum specification you defined.
For example, a much smaller motor can still move it up a 10 degree hill incline, but don't expect the same max velocity and maximum acceleration. Unless of course you define it in the RMF calculator. Also, at maximum expected velocity, the acceleration is zero (although acceleration is needed to reach that velocity). In your previous calculations you were giving it an ability to accelerate at its maximum velocity.
I looked up a wheel chair myself to find typical specs . . .http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200108642009
It has a spec of:
1.16 inch wheels
maximum speed 5.8666 (4mph)
Now, that means it'll do 4mph with perhaps a child on it, but not some 130kg guy on it. Also, since it's max speed, acceleration has gone to zero and incline must be 0. In theory, holding a velocity requires zero torque, but some small amount will be needed to counter friction.
I got an RMF of ~15 lb ft rps. This would be maximum RMF (power) the motor could do, no matter the velocity/accel/torque you defined.
If I showed you a 3D graph representing acceleration, torque, and velocity, it'd all make more sense. At the maximum spec of a motor, as you increase one number, the others respectively must be decreased.