What you have read is correct. Not all printers and print servers are compatible.
If you've already got an Apple and it's working, that's just fine. But, don't expect it to work forever and with any printer that you will buy later. That's not guaranteed.
If you have brand loyalty to a printer manufacturer, look for a server that they make. HP makes both wired and wireless print servers.
Personally, I'd use wire where I could and wireless where running Ethernet isn't practical.
I want to get a wired print server (which I will later, connect to either a wireless cable modem or a router, to give it wireless access). For the short term, I need to connect to this print server, two computers (a desktop without any wireless connection, and an Inspiron laptop that is two years old and has done fine giving me wireless access many times).
I decided to go with an Aiport Xpress, but after opening up the box, I saw only one usb port, which would allow the signal to go from the unit to the printer, but no way to connect my desktop (needing its own usb port) to the Xpress.
One of the reasons why I went with Apple, was that many of the reviews on other print servers were saying that they would only work with a limited group of printers, and while I don?t envision buying another printer in the next few years (I just got a laserjet 1018 2 years ago and its working fine) I?d like to not also have to get another print server, if I ever do buy a new printer.
Are there particular print servers that work better with a large range of printers? I read reviews from Dlink and Linksys and it seemed like they would work ok on some printers but not others.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic