Zitat aus den Lizenzbedingungen von MySQL:
If you include the MySQL server with an application that is not licensed under the GPL or GPL-compatible license, you need a commercial license for the MySQL server.
Und weiter:
If you develop and distribute a commercial application and as part of utilizing your application, the end-user must download a copy of MySQL; for each derivative work, you (or, in some cases, your end-user) need a commercial license for the MySQL server and/or MySQL client libraries.
In anderen Worten: Viele Entwickler von Websoftware müssten ihren Code rausrücken, den sie kommerziell vertreiben!
Aber pssssst! :)