Well, there's inevitably some crossover.

I'd say the biggest difference is that the copy on the paysite _brands_ the paysite, and teh specialness of the set of content inside, AND focuses especially hard on the close, the emotional commitment to get to the join page and open the wallet and pull out a card.

While promo stuff pushes the 'juice' of the niche, and the arousal of the idea that the promo is associated with (usually some content samples or text embodies that idea).

While expanding curiousity ('wtf' or 'let me take a look at that' feelings).

The paysite has to close, the promo stuff has to push.

It's always dissapointing to see paysites that dont seem to care about making the close.