Well according to the band, the exclamation point was never really a part of the name, so they just didn't add it when their second album released. Once they saw how upset most of their fans were about losing it, they fixed the issue. Kind of like How MxPx got their name. It was originally meant to be M.P., but a kid designing flyers used extra large x's as the periods and the name stuck forever.
I do listen to Panic! at the Disco and I happen to know that half of the members up and quit the band about 2 weeks ago, wherein the remaining members decided to tack the "!" back on for this tour.
Maybe you should invest in some research before you correct someone. :P
