I would think any hub can charge an iPad, just very slowly. The iPad draws more power than any powered hub supplies.
...and hydrazine is often used for rockets in space, but neither are USB hubs.The iPad charger that Apple sells is designed to charge the iPad and provides more power.
This is the reason.Apparently they don't exist because they would violate the USB spec, which rates the current output at 0.5A....
This is correct, any usb hub will charge the ipad, unless the screen is on then it cant supply enough juice, if you keep it plugged in it will charge, just slower.
I found this device when staying at the Argonaut Hotel in San Francisco for Dreamforce last week. It has 2 USB ports, one of which puts out 2.1 amps for tablets and 2 electrical outlets on top. I had my iPad 2, iPhone 4S and Targus backup battery all charging off this every night and it worked great. I immediately started looking for one when I got home and I just stumbled across it tonight.
Teledapt Chargepoint
http://www.teleadapt.com/us/power/chargepoint.php