Interesting observation, but it has nothing to do with the question of moral behavior.
There're also plenty of examples of businesses trying to buy as cheap as possible while at the same time trying to sell as expensive as possible. That just proves that buyers should beware.
Also, proprietary software is not equivalent to high switching costs: in fact, it's a rather subjective calculation. If you don't care about keeping your old emails, switching your E-mail client has nearly no costs, for example. Additionally, "free" software doesn't imply low switching costs: develop a large application using the KDE or GNOME APIs, and you'll find that switching is rather expensive.
In general, your argument is a red herring: Since switching costs may establish a trap, you should warn about software with high switching costs, not about proprietary software.