Mobile satellite TV is an application that was never meant to be. That’s why those antennas are so hideously expensive - they’re complicated, and there’s a limited market for them. XM and Sirius satellite radio don’t require tracking antennas. I can’t find a cite for it right now, but XM’s antennas are made by Antenna Specialists and Terk, so if you want to check those out you might find more information on exactly what type of antennas they use.
XM, at least, uses two geostationary satellites (named “rock” and “roll”) and repeaters on the ground to relay the signal into areas where satellite coverage is insufficient. Without these terrestrial repeaters you’d tend to run into the same problem satellite TV does with a lack of a clear view of the southwest sky.
To answer your question regarding that, Dob, more power won’t help in the case of satellite TV. You still need a clear view of the satellite without those nifty terrestrial repeaters XM uses. You might get a better signal through some light tree cover or in heavy rain, but you’d still have problems if the signal had to travel through too much in the way of obstructions. Frequency has something to do with it, too - unfortunately, the frequencies allocated for satellite TV tend to be absorbed fairly well by water (trees, rain, etc.)