...how about because PDA's don't come with anywhere near a comparable screen without paying $100+ more (Basically you need to get to the Tungsten T5 or iPAQ HX47xx models before you get there resolution-wise, and still not have the size or graphical capabilities), their sound is usually lacking as well, and you're paying for all sorts of capabilities you don't actually need?
Granted the guy sounds like a cheap infomercial, but we don't really know who he's talking to. For many people, they might want to stress the availability of a good-looking (both screen-wise and case design) machine that can present the material they want to as good as they can without spending a lot on each unit. There are really no other machines on the market right now that offer that--as well as providing other features they may desire (WiFi, media options) at the PSP's price point better than the PSP. High end PDA's carry a high-end price tag, and mid-range ones would not be an impressive presentation vehicle of any sort.
I'm not sure what he's on about "education-wise" though, as I'd certainly trust the programming environment and availability of PDA's--as well as the improved interaction possibilities of the touch-screen--a lot more. But I guess they're not "extreme" for nothing.