It's so someone installing the game fresh only has to download the most recent patch and not each little patch individually...
It does suck for us who've been around for every patch... but someone who has not played since like January would probably be happy about it
But you're right Akuun, you'd think splitting them up to a bunch of small ones shouldn't change the amount of update time on a new install, since you're still technically downloading the same amount of data