lHere are some approximations:
RG59: down 3db @ 120Mhz / 100ft
RG6 : down 3db @ 200Mhz / 100ft
HDTV bandwidth 37Mhz
Among enthusiasts it is common to believe if x is enough, then 10x is better, and 100x is better still. In engineering more is not always better. RG59 provides almost 3x the needed bandwidth for HD signals, so is fine for component cables for HD signals. It is easier to pull because it is smaller, and takes up less room.
My plasma, which I run at either native rate or 720P and 60 Hz, is wired with 35' of high quality minicoax. (Slightly smaller than RG59). It is more than adequate for the application. I chose this because I had to run wires behind an outside wall, and wanted two bundles of RGBHV, two cat5 lines and 3 speaker pairs.
Honestly, there is nothing wrong with using RG6. The added bandwidth can be a double edged sword, but it's usually easy to deal with. If you have a very high resolution monitor that you run at high refresh rates, or very long wire runs, RG6 becomes more attractive. Additionally, you can run broadband through RG6, but RG59 is more suited for baseband.