There is a sense of "credibility" to the short trunks. Look at all the world champions who wore short trunks compared to the ones who wore long ones.
Some just look better in the long though.
Jericho, IMO, did.
And don't say that too much, or Edge will be the next to lose the long trunks.
It took me forever to get used to Triple H when he ditched the long tights in 1999. Macho Man Randy Savage is a unique case, going from trunks to long tights.
Yeah. Savage was unique in that case.
Though when he went to long tights, he lost the cool robes that he would wear to the ring.
EDIT: One style of look I wish more wrestlers would use is the Bret Hart style...long tights with trunks, as well as a classic style wrestling singlet top.