I'm sure it's a historical artifact more than a requirement, especially considering how some improvements made to C++ are trickling back into C (i.e. '//'-style comments) if only because of popular demand. The "correct" C example, using backslashes, is reasonably:

char *foo = "This\n\
Is\n\
Rather\n\
Tedious";
[download]

I suppose that earlier and/or less robust C compilers would not comprehend the concept of a string being continued onto a second line.

I'm sorry if you mistook my unfortunate "ignorance" as being anti-C. I meant nothing of the sort. I'm rather a fan of C++.