Of course, the more general form, exp(x) = cos(x) + i sin(x), is much more useful.

As you might imagine from my username, I've thought about this issue a fair amount. I think it's simply that we're exposed to the raw, un-spellchecked ramblings of computer programmers at a higher rate than those of non-computer people.

The computer-literate might have more math than language skills; and they're also the ones filling websites, email lists, (and especially Slashdot) with their musings. The English majors and other more literate types are using the Web too, but perhaps with fewer, more considered posts.

Just a theory, though.