Why do Jasper and Rosalie have the same last name?

Rosalie's surname when she was human was Hale. There is a simple reason for why Jasper and Rosalie aren't Cullen, wouldn't it be kinda creepy for Alice Cullen to date Jasper Cullen? the slagging would be a bit much. So all the couples have different surnames, except obviously for Carlisle and Esme, as they are the 'parents'.

If the Cullens ever move from Forks and start in a new school, Bella will probably take a different surname to Cullen.

hope that helps