I lend credence to the "it's too hot" thing. Might be because I live in Arizona. Remember how hot the climate is in most of Africa.
Remember that guy on Survivor who fainted and fell into the fire? I noticed at the time that he was the baldest, and the only bald one not wearing a hat. That forehead makes like a big solar panel.
I actually read the article, and misread "it's too hot" as a reason we kept head hair, as opposed to the reason we lost body hair.
Actually you were more right the first time; the article said maybe we lost body hair to swim, but kept headhair so we'd be cooler other times, like treading water I suppose...
I'm amazed at how long men have been shaving. Seriously, I use the latest shaving technology and can still get burn and bumps if I don't watch what I'm doing. I can't imagine hacking at it with primitive tools...
I think we may not have been as concerned with getting a super-close shave, as we are today.