Your right, its not sponsorship. It is exchanging advertising for discount though.
If you have a couple of websites on your jersey and you get discount, thats all good. You arnt personaly indorsing the websites, it is just an agreement of mutual support.
Although I can understand that if it was to be seen as sponsorship it would be hypocritical to have more than one of a similiar or even competing websites.
Even if somone does have loads of names plastered all over their jerseys, why is that a bad thing? Some people will pay extortionate amounts of money to have clothes with brand names on, if you can wear the names and get discount from them, then why not?
It could be that some people think that the more sponsors they have, the more people will see that and so think they are perhaps a better team? A way of gettin respect from people who see you wearing that jersey with all the names on it. If you are "sponsored" by that many people, you must be good!