Chesh admits that his theory is only speculation, but cites the timeline of the shutdown and previous Sony actions as evidence:
Now, this isn't the first time Sony has fought back against the PS3 modders from getting on PSN. A couple of months ago we had a utility called f*ckPSN that changed the necessary header information that was being sent to Sony to allow modified consoles back online. We were able to use it for about a month. Then came the new TOS, the mass e-mail to PS3 customers, and software update 3.56 and 3.60. So, once again, yes this is all speculation, but it is speculation based on previous actions and known facts.
Sony has yet to post another update since this morning, when it stated that it had no timeframe, but that it is working to get PSN services "back online quickly."
Apr 25, 2011
