Well, mostly I pay for porn at the webcam sites. Surely, you can sit there all day and watch the girl without making any payments, even you could chat with her for free without giving any tips, but that's not very classy. After all the models entertain all those fuckers and for that I think they deserve some tips.
Well.. adult webcams are tricky. If you are not going to pay, then the provider will just relay the pre-recorded content again and again (and some idiots will never realize that it is pre-recorded). On the other hand, if you want to go "interactive" and if you want the girl to perform according to your wishes, then you might be needed to make a small tip.
Exactly they are doing the same. They are just showing same content again and again and if you want to get into private then you definitely have to pay a tip or else the girls will not entertain you