Actually, the primary documentation for glibc is available in the info format (preferred by the gnu project.) You can check it out by typing "info libc" on Linux (or by googling [info libc]), and I really encourage you to do it, because you may learn new and interesting things (I know I had when I first discovered it.) Most man pages on Linux have a note saying that the documentation in man format is obsolete and the info format should be used instead.

This is not to say anything bad about OpenBSD which I have no doubt is a great system, just that the comparison is somewhat unfair.