Usage of the BSD or MIT style licenses implies that this is the wishes of the author. If that's not the case, the type of license that was chosen is a poor choice.
I posted this somewhere else, but I'll repost it here:
The BSD license allows and promotes the idea that anyone can use the code so long as they say that they are using it. That's it. If someone took Growl code, which is BSD, and put it into some shareware or commercial code (which has been done), I really don't care and in fact think it's all for the greater good.
GPL code on the other hand I don't think should go into any application unless it is relicensed by the person who wrote it.
For instance, the Bubbles in Growl were originally in Colloquy. Karl Adams and Timothy Hatcher both relicensed the Bubbles code to be BSD licensed.
Now, if the core of something is open source or not, it shouldn't matter. What should matter is how the original author of that code intended that code to be used. The BSD is quite clear in this regard, and so is the GPL (albeit a lot longer and a lot more open to legal interpretation).
So if David wants to sell a UI on top of an BSD core, he is well within his legal rights to do so, and is respecting the wishes of the original author. The problem he (Acquisition) and Justin of Proteus got into is when they used a GPL core. They got around the "virus like" qualities of the GPL by using something to separate the way things work, but it's still kinda cheesy.
As someone who is about to start selling shareware though, I'm sort of biased, but I'm also rather opinionated about the whole topic. I believe it is well within the right and the wishes of any developer who licenses their code as BSD that their code can be reused for whatever purpose so long as they are given credit somehow. What the folks who are using these BSD licensed libraries are doing is not immoral, but rather smart.
I also think that David tends to get UI right in general. I think Julian does too.
I also think that if a tool gets the job done better and looks better, then it deserves the cash.