So there is actually new evidence since we had this conversation. Bisexual men do exist! Past studies found that the men they studied who identified as bisexual weren't.

The different results are likely due to the different procedures used to determine the participant pool. The 2005 study took it's sample of bisexual men mainly from college campus LGBTQ student associations while the more recent study advertised on craigslist M/F for M and, on top of that, refused to include anyone whose claim to bisexuality they didn't believe.