This is why the Microsoft monoculture is bad
Back in the '80s and early '90s, people coped perfectly well with competing computers and operating systems. Sure, an Amiga was a bit different from an Atari, which was a bit different from a PC, which was a bit different from a Mac, which was a bit different from an Archimedes... but so what? People coped, just like they cope with the way every washing machine or DVD player today has a different interface. When you started using computers, you became computer literate, just like everyone's more or less washing-machine-literate and DVD-player-literate. And once you're literate in a technology, you can learn to use any form of it relatively easily.
What the Windows monoculture has done is to destroy computer literacy among most users. Now, instead of learning to use a computer, people are trained to use Microsoft Windows. Instead of learning about launching applications and using word processors, they're trained to click on the big button at the bottom left of the screen that says "start", then to click where it says "Microsoft Word". And so as soon as that button turns into a picture of a foot at the top left of the screen, and the icon they're looking for says "Word Processor", they're left bewildered and uncomfortable.
Of course, this has now bitten Microsoft too: it's one reason why Vista and Office 2007 are so unpopular.