Would you feel better about (($a|$b|$c|$d) >> 8) == 0? The intent is to check that each component is one byte, and bitwise or-ing them is consistent with the bit-fiddling nature of what's being tested.

If 256 weren't a power of two, there wouldn't even be a presumption that it might work.

It's clear that you didn't see this as a bit-fiddling scenario, but it is. What, after all, is an IP? It's a four-byte string, translated into human-readable form.