Galaxy Nexus GSM works with iPhone 3G Mini SIM Card

Two years ago I switched from an iPhone to a Nexus One. When I made the change I simply put my iPhone 3G Mini SIM card in the Nexus One and everything worked and I had 3G speeds. I have recently upgraded to the unlocked GSM version of the Galaxy Nexus and again I did the same SIM card swap. Again everything worked and I seem to have HSPA speeds. Three back to back tests with speedtest.net on the Nexus One had a download speed of about 0.75 Mbps while the download speed on the Galaxy Nexus was about 1.25Mbps. I know there are people out there getting much faster download speeds with the Galaxy Nexus on GSM but I attribute that to my area.