After downloading wordpress-2.3.1.zip from http://wordpress.org/download/release-archive/, I tried to compare the published md5 [md5sum] with the one calculated for my local file. The two strings did not match.
Downloads of the other recent files (versions 2.0 and later, in both .zip and .tar.gz compression formats) made me realize that the published md5sum for each WP version is for the .tar.gz format _only_.
So first, I'm offering a patch. At http://www.twin-dad.com/wordpress-2-and-later-md5-files.zip is a zip file that includes updated md5 files for each version of WordPress from 2.0 on.
Each md5 file includes an md5sum for both the .zip and the .tar.gz formats of each WordPress release. The WP site admins can unzip the file, check my work, and replace the old md5 files with these new ones if they pass muster. Then, other users who want to check the md5sum for the zip version of a given WordPress release can do so.
Second, I'd like to ask if the developers/maintainers would be willing to include md5 information for _both_ file formats as each new version of WordPress is released going forward, instead of just for the .tar.gz format?
I hope this is not a huge burden to put on anyone, but if no one else is willing, then I'd be happy to step forward for this task (including beta and RC versions) going forward. I'm not a programmer so I can't help there. But as far as this goes, I could help.