"Because it's all about the experience"
Most people go to apple's site to upgrade, because they know apple makes it easy. Most of those people don't really look into other options, like ordering off-brand RAM, which means Apple is free to charge whatever they want.
If Crucial says it's compatible, I'd trust them. They are a well respected brand. As far as differences with Apple go: fat chance they are using the same RAM chips (Samsung probably).
I take pictures so quickly, my highschool was "Continuous High".