You can't buy an open-source project. While MySQL has (so far) distributed their code under an open-source (well, sort of) license, they follow the traditional "all development is done by employees who assign copyright to the company" model. In contrast, Sun could hire a few Postgresql developers, but there isn't any central organization which they could buy out.

Similarly, there are persistent rumours that Sun will buy RedHat; but never any suggestion that anyone would buy Debian or FreeBSD, because the later both lack any central corporate body.

Err... yes, I know. As a Postgresql user, it was nice to know they were spending some money on Postgresql, and I'm sorry that that will likely come to an end.

MySQL is available under the GPL. Nothing sort-of about that.

MySQL is available under the GPL, but MySQL AB has a history of misleading people about what the GPL license means, in order to convince people to pay for commercial licenses which they don't need.

That's what I meant by "sort-of" -- MySQL is GPLed, but where potential customers are concerned, they try really hard to make sure that people won't take advantage of that fact.