well vbulletin offers more payment options I beleive and may be more visible if users look at there vb
profile more our link is in our profile. Otherwise they pretty much work the same you come up with a charge and description. A user reads and purchases. Once they purchase they are thrown into a special usergroup you create to house the subscribers. You can in your forum and gallery categories and usergroup permissions set permissions accordingly to give your subscribers more access perms than regular users as you wish.
That in theory is how things work. Length cost features are all up to you.