Apples upgrades for iOS go straight through Apple. No ridiculous excuses about the carrier needing to test the firmware, etc...The only difference I can think of with Apple, and iOS is the fact that they announce a new version of iOS 3 months in advance which gives everyone from carriers, to developers time to test it out before public release. The fact that Samsung has Jelly Bean ready, and now we're only waiting on AT&T, and Verizon to approve this release is in fact pathetic. Don't get me wrong, I still love my device regardless, but holding back a release until they're ready makes no sense. Project Butter, and Google Now is all I care about, don't want to be bothered with rooting my phone either.
Don't forget that iOS has not really evolved all that much the past two versions. The move to iOS 4 brought a bit more multi-tasking, but then has only added a few features, but not really a lot of changes to the fundamental OS. Stagnant platforms are a lot easier to deploy updates for, since there is primarily testing of applications. Android on the other hand has seen a HUGE change from 2 to 3 to 4. Notice that going from 4.0 to 4.1 to 4.2 will require a lot fewer fundamental changes, so we SHOULD see updates released more quickly. Apple also does its own support, and you may have noticed that AT&T will often send customers to Apple to deal with issues. If Samsung wanted to set up the support facilities to deal with customer calls/issues, I am sure they could charge the carriers more for devices.