Those planning to extend past the "standard" reception time, it seems like it would make more sense to keep the reception going rather than stop and start elsewhere. Many venues have no curfew at all, and food and drink is still flowing on your single per person charge instead of guests paying their own way later. Anyone who wants to leave early can do so. They both can easily have the same party vibe, and you don't have to worry about transportation, making sure everyone gets to the right place because they are already there.
What makes the after party elsewhere more appealing to most than staying for a few more hours having the same festivities?