Why not also, while at it, disallow spaces too? They can very easily cause problems too, if you split by spaces instead of newlines. Quotes and backslashes obviously are also bad. How about all of non-ASCII unicode? That'd break all code assuming character count equals byte count, and can probably cause buffer overflows when people count correctly.

Any characters you disallow still allows people to fail on some other character. Sure, it'd decrease the likelihood of messing things up by some amount, but that's a half-assed solution at best, and would make people check for mistakes less at worst. Imagine if intel fixed the pentium FDIV bug by only fixing 30% of the wrong results.