Another related article that Jeff L. pointed out today was this:
http://instructables.com/id/Modify-a...an-iPod-iPhone

That article nicely further explains the Apple charging standard:
a) 2.0 V on D+ & 2.0 V on D- tells the Apple device it's a 500 mA port
b) 2.0 V on D+ & 2.8 V on D- tells the Apple device it's a 1 A port