I've just started out with Drupal. I'm still alpha testing my site, found out the hard way regarding using the correct module versions, and already dreading future upgrades.
My suggestion is for a way to know the version numbers, particularly of modules and your Drupal installation, without going looking through the files themselves, which in most cases mean ftp. Of course, if you maintain the site, the onus is to keep a note of them. What I do is to keep the downloads of the gzip files so I can tell which versions I have.
But what happens if you lose them, or take over somebody else's installation. Ftp downloading and reading text files are a chore.
Let me apologize first as I haven't done any major php coding (only changed a line here or there, or code-copied), or if this is being worked on, but I hopefully can point someone in the right direction.
In well-coded files, the second line usually contain the Id's so I think this is the only location for the version numbers. The system database also holds the info on the modules. I can think of 3 ways on how to get the numbers from the browser interface:
1. A script to read the second line from each module, either one-by-one (quick) if you make the link from the module settings page, or the whole gamut (lots of file lookups). Reading the text files however doesn't sound like good security, and would take lots of php filters to get to the number.