It's not that plants can't grow under incandescent, it's that it's very inefficient. Florescent puts out many more lumens per watt, so you are getting more light for less energy.
Also, incandescent produces a lot of heat. It can be very dangerous to your fish by causing temperature fluctuations and/or overheating the tank. People who use lights that produce a lot of heat (there are many different reasons) must use extensive cooling systems to protect their fish.