A lot of developers and interested parties in the FOSS community have raged back and forth over the propriety and legalities about charging money for the supposedly open source software itself, and/or distribution of said software, and/or services and/or maintenance and/or bug-fixing for the software.
Mark had gotten tipped off about an upcoming book that mentions WordPress being not merely open source, but a variant of shareware. Mark proceeds to set the record straight in his post; and rightfully so, given that we use WordPress here, too.