To me, these are just another carrot right. I understand that it's not a real beta. What it is though, is an opportunity to get familiar with the system/UI/options/etc. so that you can hit the ground running on day 1. I also think there there is a modicum of information the developers get regarding any game breaking things that may crop up during those weekends for their inevitable day 1 patch.
I don't mind paying for this. Every game does it nowadays. People will pay for it, like me, so why wouldn't they do it?