Multiple 2A USB Mains powered chargers
While the USB 2.0 standard doesn't really apply to chargers (USB 3.0 does have Battery Charger Specifications), manufacturers are free to go out of spec. And there ARE chargers that do such. While I don't have a link to it, Walgreens had a small dual port power cube, with a high current iPad (2A) usb port, and a 1A iPhone charging port. You could use both at the same time, either 2 iPhones, or one iPad and one iPhone.

A quick google for 5 Amp Usb Charger also shows some results. They exist, but just arn't common. And honestly, they don't need to be. 5 dedicated 1A chargers on a power strip is just as easy or cheap as a dedicated 5A usb strip.

Even better, google Multiple iPad Charging Station.

The PowerDock 5 is a 5 port, 2.1A per port, iPad charging station.