But I think a lot of people are like that and site owners that ask people to register should realize that they lose a certain percentage of people that way.

Not only do they realize it - often, that is the very reason they ask you to register.

In the old days, there was lots of free or cheap webhosting with unlimited bandwidth. No more. And Poser files are big. Hosting a popular Poser item can be very expensive. A lot of web hosters charge you big bucks if you go over the limit, or lock your site so no can visit until the next day, or week, or month. (One month, I ended up shelling out $150 in extra bandwidth charges.)

However, it seems only polite to mark items "site link" or "registration required" in the comments or on the thumbnail. That would save our time and their bandwidth.