Virtually all memory card readers are in this category of requiring more power than the N800/N810 will put out, thus the powered hub approach. There have been reports of one or two "single" card readers that do seem to just squeeze by, but apparently they vary from manufacturer, type of reader, and just plain old luck. Do some searching around the forums here if you're looking for specific makes/models that others have confirmed to work.

Thanks!
-Rob