I'm sure that portability is a major goal, but "from day one" isn't. Better to focus on correct, high quality, readable code first and then deal with a portable version. And OpenBSD C code tends more toward generic UNIX than some others, so shimming is less painful than it could be.
There really are a lot of parallels with OpenSSH's history. There were the "Oh, God! Theo forked SSH!", "It's just OpenBSD, who uses that?", and all the rest. Now everyone uses it, and it's a good thing. The wait time for it to be ready and available to all platforms was a small price to pay, well worth it, and quite small in retrospect.
There really are a lot of parallels with OpenSSH's history. There were the "Oh, God! Theo forked SSH!", "It's just OpenBSD, who uses that?", and all the rest. Now everyone uses it, and it's a good thing. The wait time for it to be ready and available to all platforms was a small price to pay, well worth it, and quite small in retrospect.