Are all iPhone/iPod accessories are compatible with iPad?
I believe the lack of accessories may be due to the power requirements of the iPad.

The iPad comes with a 10 watt charger while most iPhone chargers are only 1 watt. According to this article lower wattage chargers will work, they will just be slower.

http://m.wired.com/gadgetlab/2010/04/ipad-battery-charging/