I tend to believe that lesson plans builds value. Lesson plans take time and energy to develop, and if you can find people willing to pay for it, then more power to you. The one part that is a little questionable is if the school has rights to the material (and / or associated revenue). In the private sector, there's been plenty of intellectual property cases, where any idea developed on company time is company property.
If I were a teacher, I would do similar to the last teacher mentioned - I'd share it freely with friends, co-workers, etc, but I'd also sell it online (ideally under a Creative Commons Attribution-Noncommercial-Share Alike license). In other words, free to share, allowing others to build off of it, but not allowing others to profit from it. In reality, with a loose license like that, anyone that did pay for the content would basically be giving me a donation, since the material would be free to share. In fact, I would probably post the material on less commercial sites, and try and use a tip-jar model. So, a bit more liberal than most of the teachers who cited in the article and are selling their material online.
One of the big reasons I like the idea of selling lesson plans as opposed to sites that allow teachers to just share lesson plans, is that it encourages teachers to polish their material. Free lesson plans, much like free software, can vary wildly in quality. The open-source software model is a great parallel for this though, in that good software rises to the top, and people can still make money even as they give away their software.
The value of good lesson plans is that they can be used to teach, as well as to share ideas and improve. When I was teaching, I was fortunate that the math department head shared all his lesson plans, as did his predecessor. By the time I had the material, it was very well polished, and was perfect for me as a long term substitute, who wasn't quite sure about pacing, pedagogy, etc. The binder I got had daily lesson plans, with all the worksheets, etc for each day. Now, I didn't teach straight from these lesson plans, as obviously you have to adopt the material for your teaching style, your students, etc, but they provided an excellent base.
Creating lesson plans are one of the reasons there are such low retention rates for new teachers. Good lesson plans are hard, and when you're starting out, just developing classroom poise and presence are difficult enough. Have lesson plans provided to me allowed me to focus much more on teaching, and really work on my delivery and teaching style.