The amount of time people have to waste on PCs waiting for the OS, doing anti virus stuff, staring at blue screens of death, rebooting because it's got confused, etc etc
But this isn't an OS war thread :) Suffice to say, "It's still just a PC" is completely missing the point. A top class restaurant still 'just' serves food, but you can't really compare it to Macdonalds.
And to many people, Apple are in a class of their own. If I didn't currently use a macbook, I'm not really sure what else I would use. Some of the Asus laptops look ok enough (At least like cheap copies of Apple design), and maybe Ubuntu is getting mature enough on the desktop to be useful, but there's not an obvious alternative.
Regarding "I don't see the revolutionary part", you don't have to be revolutionary to be better than everything else. People use Apple stuff because it works and is well thought out. It stays out of their way and lets them achieve what they want to. It's designed to make everything as seamless and useful for the user as is possible.
Some people just want a car to get them from A to B. So they buy a standard boring crappy Ford or something that looks like a dog. As long as it gets them from A to B, they're ok. Others actually love the 'driving' bit, and enjoy it, as well as having a thing of beauty. So they buy a better car. Same is true with computers (And most other things).