Because crappy Macs have no Home/End keys (or they don't work as such).
It's not that Macs are crappy, they just have different key bindings. I regularly work with Macs, Windows, and Linux for development and I've just learned to use the different key mappings.
I don't think I'm quite as proficient in any one system because of that, though. For example, I have avoided learning the Emacs key bindings for use in Mac/Terminal. (I don't want to try to remember TWO bindings for Mac, plus I learned vim first so usually avoid Emacs.)
Yes, other systems have other key bindings, but why do common things like jumping to the begin/end of a line need a key combination? And why aren't the characters written onto the keys? Every time I have to type some code on a Mac I have to press all the keys in order to find { } [ ] etc. At leas I learned not to quit the terminal when I want to enter a @ by now. Whose brilliant idea was that?
In contrast a German PC keyboard: http://www.buypcsupplies.com/images/cat/38568_xlargenss_ndo4...
However, I prefer a Microsoft Comfort Curve keyboard, but I can't find an image of the German version right now.