Hm, I thought they quit relying solely on the CPU / bus clock years ago - most software (and drivers) use clock ticks (1/18th of a second, or 55 ms) as a time reference... so the speed of the CPU clock shouldn't matter. Heck, find any old DOS game (like the origional Tetris I have on a 5.25" floppy) and try to run it on anything faster than an 8088 - the pieces fall so friggin fast even on the slowest speed
The actual pen itself probably isn't the problem, just the software driving it. They need to update their drivers, and possibly state incompatibilities on the box/advertisement - just as good business sense...
Justin