None of this was intentional. FTA:

"Update: Consumerist has updated their post with a message from Zecco claiming that it was not an April Fool's joke, but noting "Some clients may experience incorrect display of Buying Power and Account Balances." It's not entirely clear how those "incorrect displays" were apparently off by millions in some cases."

Even more important than the question of what would motivate an ISP to block services is the question of how they would go about doing it.

The FCC recently in a formal ruling that Comcast's P2P throttling was illegal and ordered them to cease and desist (see http://news.cnet.com/8301-13578_3-10004508-38.html?tag=mncol;txt for more info).

So this effectively puts a hamper on "limiting file sharing services" as a blanket policy. The RIAA will likely have to instead focus on individual users who are doing specific things. This basically just takes their problems out of the courthouse and into ISP corporate offices.

Where are you getting these restrictions on prior art from?

There may be a rebuttable presumption of validity if you want to apply the same piece of prior art in the same way as it was used earlier on in the prosecution history, but there is nothing preventing you from using it court. Think about it: it would be fundamentally unfair to not allow someone to use something as evidence in court simply because it was brought up in an earlier ex parte proceeding.

As for the "nobody does it"--do you know the different in cost difference between a third party submission versus an infringement suit in court? We are talking thousands versus millions of dollars here.

There are certainly plenty of reasons why someone would prefer to take an issue to the courts, but sitting on a clear, obvious piece of prior art is not one of them. Of course, patent trolls are the exception to this rule.