MySQL caused a bit of a stir where I worked for the same reasons mentioned in the article. It is not always about doing the legwork, as anyone can pretty much take a few hours of research to find out licenses, variants in code and so forth.
What IS the problem however, is the fact that the GPL is a complex legal document and some companies don't want to pay the fees necessary for a small battalion of lawyers to confirm its use on a server platform or within a product. Its polar opposite the BSD license however is far easier for anyone to interpret and has a lot of legal precedence behind it.
The MySQL dual licensing issue reminds me of another project I encountered. iText PDF (http://www.itextpdf.com) is a Java open-source license that was traditionally released under the Mozilla Public License 1.1.
Oddly enough, just as their tutorials disappeared when the author of the library published a book. To which is used exclusively when asking for help in the forums, they also changed the license to the AGPL.
This seemed to be a way to force companies into buying their dual license. Apparently a lot of people used their product on a back-end servers to generate PDF invoices and so forth. By forcing the license change it meant that their changes to the code would have to be released and the viral nature of the AGPL forced the hands of many formerly legal products.
Fortunately, their MPL licensed version is only a few months older then their new code and oddly works with their Tutorial files they have hidden away in an old archive on Source forge.
Not that myself or my organization was opposed to licensing legally. However when you have a small, no fee, in house product being distributed within your organization and they are looking for 100$ US or more per instance for licensing fees, it rather makes it a hard pill to swallow.
MySQL had the same problem some of their fees seemed to range in the 300$ US per instance depending on the type of licensing involved and overhead of the company you used to get them. Some individuals at our organization recalls getting Oracle licenses for that price!
In a way, are these open source products or are they simply using the moniker as a way to attract people and force them into costly solutions?