I think you can safely say that most SDIO things will only work on PocketPC's, as that is all the manufacturers seem to care about when writing drivers for them. Some of the Wifi cards work on other devices, but not many.
For example, the Zodiac was dual-SD friendly (you could use 2xSD cards, or 1xSD and 1xSDIO) and fully SDIO from the start, but the only SDIO card it supported was a single Wifi card that is difficult to get now.
One thing to remember: SDIO is only another bus - it's a way of transferring data to and from another device. What data is transferred has nothing to do with SDIO - it can be (and normally is) different for every single device. There are some device classes you can buy/use so you are compatible (and thus you only need to get a driver for that class), but not every manufacturer uses them.