They probably didn't want to completely change the original name, but at the same time make it look more normal for English audience, so it came-out looking confusing like that.
Vegetto looks kind of like Veghetto while Vegeto sounds like a typo for Vegeta. Vegito has some weird I that came out of nowhere and Vegerot just sounds plain retarded. Whatever his name is, the guy just can't catch a break.