I've never had trouble connecting a Mac to a WPA/PSK or WPA2/PSK network. And, as others have said - that's what the Airport Extreme's WPA "Personal" mode is. I also seem to remember that, at some iteration, the Airport Utility (or older Admin Utility) actually used the terminology "WPA/WPA2 Pre-Shared Key".

I'm sure the hint's author had trouble connecting to one such network, and figured out how to get it to work. But he shouldn't have extrapolated one isolated circumstance and assumed this to always be the case.

However I'm also sure this information will be useful to someone who finds himself under similar circumstances. It might be worth rewording the hint (maybe something along the lines of "if you find your Mac unable to join a WPA/PSK or WPA2/PSK network...").

Thanks for your comment above explaining what a PSK actually is.

As for the author of this tip, I suspect English might not be their first language. What they meant to write isn't what they ended-up writing.