Possibly the original non-free version was similar to the OpenBSD, or perhaps the GlibC developers took applied this rule where not strictly necessary. Don't know; just offering a potential clue as to why the GNU version is so different.
When they say "Unix," I think they mean the original, proprietary implementation. I don't think this is the reason why they differ. The BSD implementation is the obvious one. The GNU library version is optimized for a 32-bit processor. Given their domains, that makes sense to me.
