The thing about casual discussions like that is it's easy to build a narrative without actually providing much substance. Joel's essay doesn't discuss Microsoft's "barrier(s) to exit" that Office itself didn't give up completely until last year (cf: Open Document), and Windows itself has yet to yield (it is still the dominant OS, by far, in the desktop and laptop markets).

Sure, "barriers to exit become barriers to entry" is applicable in some contexts, and for some part of a potential market it will be the barrier that keeps those customers away. I wouldn't dispute that. I would dispute that "barriers to exit become barriers to entry" be treated as a universal maxim applicable along all businesses and products. It's just as much of a strategy mistake to make as assuming the barrier can't exist in the first place. It ought to be considered; not treated as a key issue until or unless the data suggest it should be.