most of these sites are news blogs that do not offer any type of product or service, so it's obvious that they're urging their visitors to participate more so that their ad views can go up. does this violate adsense's tos?
Unless they state that they want you to click on their ads or they ask you to join for the purpose of increasing their ad views it is not against the TOS ad Adsense. What you are saying is basically what every website and blog owner is trying to do. The more views the better chance for clicks and the better chance to make money. The more people visit and join the more traffic you have and the better for everyone including Google.