One thing you should learn about electrics is that there are no generalizations. It's true that you can't use a 3S LiPoly on brushed motors, but only SOME brushed motors, not all of them. Many brushed motors are quite happy on a 3S LiPoly, and many more can be used, if you keep in mind that the motor's lifespan will be shortened signifigantly.

The problem with any of the *calc programs is that they can't effectively tell you what to use. Just blindly going through the wizard, Motocalc, for example, will give you thousands of combinations, most of which are pretty wacky to the educated eye. The true value in a calc program is in verifying the behaviour of proposed combinations before you actually try them. They're not 100% accurate, but they're close enough to get you in the ballpark without frying something.

Personally, I find the advice and shared experience of others, along with the manufacturer's motor data and a pinch of salt much more useful, and tasty