I spent a week deleting code I couldn't detect a use for. I nuked nearly 40,000 lines and could not discern a difference in functionality (though, couldn't be certain since I hadn't completed the test suite.)

I don't think we deleted 20k lines. Probably more like 5k.

However the kicker was when deleting something that seemed harmless enough broke something. In that case, it was a comment. We're not talking about smart comments here. We are talking about comments that are parsed and used by the application at run-time for actual logic :-P.

Oh, and when we added test cases for rounding numbers.... the test cases failed....

Regarding the role of language, I would much rather be maintaining bad Perl code than bad PHP code.....