one word, stability and longeverty (spelt right?)
OK so it is two but what the hay!
The Palm is a more stable device, I work at PC World and we have a display of PDAs 2 Palms, 1 Sony, 7 PokPC (Compaq, HP , Tosh, and XDA). None of them have any extra s/w installed, only what they come with out of the box. The PokPC's do lock up for no apparent reason, some (Compaq's) more often then the others. The Palm & Sony rarely lock (they have but not often).
Longeverty(?)
Batteries:
Palms will last for days-weeks
PokPC hours-days
Oh and PokPC are Microsoft based so need huge memory (32-64Mb) and large amounts of processor power.