But that's the thing we don't really have an interface to upvote the cross-post ... they'd have to use a different interface if they want to upvote the cross-post itself.
I mean they can go to the full post and try to upvote the crosspost itself if they want so there are ways but you kind of have to go out of your way to try to upvote the crosspost itself.
Basically if you've already upvoted the original then it will show on the cross-post because the cross-post is showing the stats of the original.
I just cross posted for the first time, think I understand how it works now. Thanks