100kb is 100kb any way you slice it... if you didn't save it as .mp3 you would've found some way to get it in there like saving it as a zip...
Added mp3 to the list, although not many options of uploading are available since the maximum file size is 100kb (incidentally, this limit takes care of most mp3's that are recorded of copyrighted material... yeah, two birds with one stone!

)
This limit is a precautionary measure until we figure out what kind of disk space usage this site is going to cause.
If 10 people eventually end up posting 100 100kb attachments, that's 100mb disk space used. Now, that is not gonna fill our disk space usage up, but it is a lot of disk space. It is spread across 1000 attachments, though, so the disk space is more wisely used.
If the file size were increased to something like 500kb, it would take a lot less attachments at the maximum size to take up the 150-200mb of disk space we've got left, and before you know it, we'd have to disable the attachments.
There's no way to know how many people are gonna attach files and how many files they're gonna attach, so for right now the limit is 100kb. In the future, if we happen to get a larger web account (dedicated server, anyone?

), or if we get a good idea that people aren't going to abuse the attachment system as heavily as we thought, the attachment size might increase.