The 500gE model isn't available in Australia, but I am curious as to what's the actual differences between this and the older 500g model?

Is it because of the new wireless bit to support a larger area of coverage? WPA2 support? Maybe USB 2.0? Is everything else pretty much the same?

If it is, I plan on getting the Mitsubishi R100 (OEM of 500g), as it is cheaper.
(Both the 500g and 550gE models use Linux, and that's my prime requirement)