I was going to suggest reading the source code, but I just checked myself and title changes like this are in an unreleased "scrubrules" directory.
The unconditional capitalization of the first letter in submission titles makes "IPhone" and "JQuery" look pretty silly.
HN also automatically capitalizes the first character of your submissions title (“iPad sucks!” turns into “IPad sucks”). You can edit, though, and correct it. Maybe that’s also possible with the exclamation points?
The next question is... does HN also remove the interrobang‽
You'll also notice that numbers often get edited out of the start of titles (e.g. "10 Ruby Tips and Tricks" will probably become "Ruby Tips and Tricks"). Someone is definitely watching us :-)