The problem is, only one person has to figure out how to build it, then if it's real free and open source software, they're legally allowed to distribute their own unofficial builds over the internet. The original XChat developer decided that it was too much effort to develop XChat for Windows, so he charged for it, which resulted in silverex's free X-Chat 2 builds and the HexChat fork.
I don't think users respond well to this either. You're essentially splitting your userbase into a group of people who know enough to build it themselves and receive it for free, and a group that have to pay, and I don't think people in the latter group appreciate being in that group.
Hmm I didn't think about that. I guess that's a genuine option for popular applications. Personally, for some unpopular applications I've tried to compile, I just gave up if the standard `./configure && make` didn't work.
As for your second point, I think it comes down to two things: if the user's time is more valuable than their money, and two, if they can get support for the paid product (at least that's how I've seen some products doing it), so it's not as if the paid is without it's benefits. Your Hexchat example shows how important it is to not alienate your users though.
I don't think users respond well to this either. You're essentially splitting your userbase into a group of people who know enough to build it themselves and receive it for free, and a group that have to pay, and I don't think people in the latter group appreciate being in that group.