That's because ESPN 3 games are dependant upon your internet provider, while WatchESPN is dependent upon your TV provider.
Correct and that is the case for most all providers except Time Warner Cable and Brighthouse. They made a different deal much later then most of the other providers; they never offered only ESPN3 to broadband customers back when many others did. They were the first to make a deal and it was called ESPN Networks at the time, which is now WatchESPN. However, they are able to access the ESPN3 content including the exclusive games but they must have TV service with ESPN included in there package.
You'll notice both TWC /BH are not on this list:
Do I need an ESPN video subscription to view ESPN3?: http://www.timewarne...ideo-espn3.html