Perhaps the version of Lion installed on the new MBAs is truly a different build (not uncommon, but surprising given they both came out on the same day).
Indeed this is true. The version that ships with the 2011 MBA is 10.7 build 11A2063, not 11A511. The build on the MBA likely contains the drivers for the new chipset, graphics, and Thunderbolt drivers for the MacBook Air. Also Bluetooth 4.0 drivers.