The Android Developer Blog called it "an ID check at the airport which confirms a traveler's identity but is separate from the security screening of their bags."
From the mouths of rubes, I guess. The ID check at the airport has zero to do with safety or security and everything to do with the airlines' business model (no secondary market for tickets), enforced by government.
I had to laugh out loud:
"In practice, you'll encounter other constraints well before these theoretical limits, such as S3 provider limits, performance considerations with billions of objects, or simply running out of money."