If they are built in sequential order then often people really want lower numbers.
Reality is that most Sterns are built in random order and then they slap on the LE plaques.
Also get guys that are completists and like to get the same number game (Woz #44, TH #44, DI #44, etc...)
I personally dont care enough to pay extra but it can be fun to get a specific number (#7, 13, 69, 420, something meaningful to you)