even if the number did come sliding out of his ass (not meaning any offense, I really don't know if you've sources or not), I think it's a good guess that there's a non-trivial demographic in that situation
Yeah, sure. I wasn't trying to discard that point. But I do think a number like that should be sourced. Otherwise, stick to something like "a lot" or "non-trivial demographic".
50 million people access the internet from work on locked down computers. One would hope they are current, but we know many are not.
Either way, there's nothing your user can do about it, so you can code to him or abandon him. Bitching won't help.