I'm not really sure how practical it is to sell an open-source desktop application; anyone can compile and run it for free and the 'sell support' model usually isn't viable for something as simple as a text editor.
That's assuming that it's a program written in C/C++. If it's another language then you might have another huge hurdle to go through. (Properly installing Go in my PATH took me a while). That's also assuming they don't rely on IDE-specific make files. A lot of the time OSX applications rely on xcode project files. The other day I was trying to compile an Android app before realizing that it was written in a language by Adobe which required the purchase of a full suite.
Open source can be really limiting if the developer doesn't make an effort to document the build process well and doesn't use open tools to create the product.
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.
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.