[math-fun] Huge software upgrades, again

I'm in the process of downloading iPad 5.1 software: 729 Mbytes! I think that this must be a record for a casual software update. Microsoft will certainly want to beat them for the first Gigabyte software update. I guess that pretty much kills the data plan for the month. Has Apple never heard of rsync ? (Hint: it's already part of the Unix SW that Apple uses.)