For example there was a time when I switched a Linux distribution each month, then at some point I realized that it is getting me nowhere: I didn't know either of them in-depth or how to deal with their specific problems. So then I made a choice: I'll use only Debian, and actually learn about how to deal with problems when I encounter them, instead of jumping ship to another distro.
Its the same with text editors, I eventually settled on Vim (for a long time without any plugins), then started using plugins as well.
Sure every now and then I check what new alternatives are out there (for example there are some interesting ideas in http://leoeditor.com/ but not really comparable to Vim), but closed-source tools are never on my list. I only ever heard about Sublime Text here on HN, and even then for a long time I thought its a Mac only tool.
But with closed-source tools I just wouldn't have been motivated to stick with any of them: if there were problems with it then I wouldn't know how to work them around, or implement missing functionality, not to mention I wouldn't trust them to begin with etc.
I should say that I can't really settle on VIM right now because I'm doing full time .net work at this point. I still use it reasonably often when I'm mucking about in C at home, and I used it as my primary editor for at least five years prior to that, but my use-case was me trying to get a decent haskell environment up and running on a fresh linux VM as quickly as I could. ST2 worked really well for that.
As far as a business case goes, there's no real "vendor lock in" with a plaintext editor like this. You can always switch to something else and your files will be fine/the same. You're investing (potentially non trivial) time to learn using it, but it didn't take me long to learn ST2 to a depth that made it really handy.
I will say I'd buy a lot more into that argument for people who develop plugins.
That said I can respect the "open source" only mindset. I'm just not sure I'm that concerned about it in this particular case.