Some companies go the MySQL/QT route and use dual licensing.
Others are scared of allowing variants of their software to proliferate. They believe that would cut into or even kill potential sales. So they keep looking for ways to weasel out of being open source while still getting free development help from all those millions of open source programmers out there who are eager to help them improve their products in exchange for a pat or two on their fuzzy little heads.
Failing that, just jumping up and down and saying, "We're open source! Open source, yesiree!" seems to be a hot software sales tactic these days. Apparently paying lip service to open source means you're good people, worth buying from, at least in some marketers' minds.
Some software products with "Open" in their names are about as proprietary as proprietary can be, though, which tends to confuse potential customers.
I have a better handle than most on this sort of thing, and I'm confused once in a while myself. Trying to sort real open source from the fakes has got to be hard on people who are learning about open source for the first time.
One thing I don't see often in marketing material generated by companies claiming some sort of vague kinship to open source is a list of contributions they've made to various projects. More and more, I find myself using this as a benchmark for whether or not a company is truly "committed to open source."
Some companies -- IBM, HP, Novell, and Sun are leading examples -- put their money where their corporate mouths are. Sure, these companies sell plenty of proprietary software products, and some of their proprietary software has open source underpinnings, but their contributions to the world's pool of open source software have been huge.
OSDL (Open Source Development Labs; where Linus Torvalds works) membership certainly shows support for Linux. Financial or other support for the Open Source Initiative or Free Software Foundation would be another indication that a company is not just using free or open source software, but is a true, contributing member of the community.
I'm not sure what should be done in the future to keep "Open Source" from becoming a marketing buzzphrase instead of reality. But one thing we can do right now is thank (and patronize) companies that really do support open source and free software. Sometimes an ounce of encouragement does more good than a ton of anger.
In that spirit, if you know of a company that actively contributes to open source or free software but hasn't gotten the recognition it deserves for its good works, please post its name here. This might be a small gesture, but it's more gratitude than most positive corporate actions ever get, and I'm sure it will be appreciated.