There is another exception to this section of the FCC rules. That means this path only has two transmitters involved and they are bolted down by never moving their locations. Automobiles may not apply. An example would be if you have an access point and a user that is a couple blocks or even tens of miles away that you want to connect to. The FCC does this as it knows that these paths will not likely not be omni directional on each end and will have less of a chance to interfere with others as well as the need to span some long distances.
Lets look at an example using the same antenna, transmission line and transmitter as above.
I have an Apple Airport that uses the Lucent Wavelan Silver card that puts out 30 mW or about 15 dBm. The antennas have a gain of 24 dBi with a transmission line loss of about 6 db. Since the little Wavelan card only puts out 15 dBm I am legal. Power over or under 1mW would be plus or minus dBm respectively. Power over or under 1 Watt would be plus or minus dBW respectively.