[Al Skierkiewicz]

General,
Sorry for the late reply. Brushless DC motors first. These fall into a couple of categories. One is used in fans, and effectively uses switched DC as an AC simulator for an AC motor. Another is a multiphase driver. This type uses several coils spaced around the motor rotor and current is switched on and off simulating a multiphase AC supply. This is the type that is used in VCR video head motors where coils are mounted directly to the circuit board. Often this type of motor has the drive circuitry and power devices integrated inside the motor and need only an error voltage and power supply to operate. Stepper motors are very similar to this type of motor and can be manufactured to be very precise in their rotational position and torque.
The rest of your questions likely come from the article you read about MOSFET behavior in a particular application. Modern CPUs generate heat even though they use MOS technology. The reason is that the devices pass through a linear region as they switch from high to low. It is during this transition that the device is neither open nor shorted (source to drain) and some power is lost as heat. Since these transistions occur rapidly in a CPU and in a very confined space (think GHz and millions of transistors), there is significant heat buildup. This will occur no matter how the device is used. As I explained earlier, the IRL MOSFET device has an "ON" resistance that is very low. At high current some heat develops due to the current through this low resistance.
As others have pointed out, MOSFETs are used in a variety of devices but a designer must still take into account the benefits vs. hazards when using any device. Many semiconductors are tailored for a particular application. The MOSFETs used in the VHF transmitter I work on are already becoming inefficient at the high end of the VHF band (Channel 11) and have significantly less gain at 200 MHZ than at 100 MHz or less. Although they are 300 watt devices, they are not very useful at UHF. The type of modulation is also a big factor and reguires different techniques for different modes. Video (both analog and digital reguire high linearity and low distortion) transmitters use class AB1 while analog audio (TV and FM) can use class C and don't require a device that is extremely linear. AM broadcasting is another application altogether. Although these devices have become very robust over the years (a static discharge from an operator stroking their hair could kill a MOSFET in the first few years) lightning discharge must be handled outside the transmitter for best results.