This is a quote from the FSF website, the FSF and the GNU foundations are closely tied and the FSF defends the GPL.
A company is running a modified version of a GPL'ed program on a web site. Does the GPL say they must release their modified sources?
The GPL permits anyone to make a modified version and use it without ever distributing it to others. What this company is doing is a special case of that. Therefore, the company does not have to release the modified sources.
It is essential for people to have the freedom to make modifications and use them privately, without ever publishing those modifications. However, putting the program on a server machine for the public to talk to is hardly "private" use, so it would be legitimate to require release of the source code in that special case. Developers who wish to address this might want to use the Affero GPL for programs designed for network server use.
It appears, from this FAQ, that the FSF considers hosting a public website to be "distribution".
The question this raises is if Drupal, being under GPL, is hosted on any webserver, that the webserver must also provide it's sourcecode. The particular case would be modifications to the core Drupal code. This source code would need to be provided "in the same location" as the program was provided.
This opens two major questions.
1. Should Drupal default installations have a folder that provides the default code for download?
2. If I make modification to code in a Drupal website, am I obliged to provide my modified and modules code for download on my site?
PS ( 3. Since technically the code contains the MySQL password, would that also be required?!? )