Yes, but AppleCare+ is one service applied to whole series. A 20% price hike on a $1000 iPhone would be $200. Equalling 4-5 years of warranty would mean you need to put in at least $600 in AppleCare+, vastly more expensive than the $200.

You're completely right that the math changes with a $10,000 laptop though. Damn that number just sounds bonkers every time :)