There's an intriguing question. I have two guesses as to why:
1) To prevent the kicking team from scoring a touchdown without possession at least changing hands on the punt, or;
2) If you're not down unless you say so, which would still allow you to carry the ball (which wouldn't make sense, actually, because of the whole "advancing the ball" rule)
In any event, let's not lose the focus of the rule. It's split between receiving and kicking. From what the poster said, if I have the ball on my own 1 and you block my punt, then I grab the ball in my own end zone and run out without getting out of it, then it should be a safety. The rule here is shown when I'm punting to you and you're close to your own goal line receiving the kick. If I can't keep the ball out of the end zone, it's a touchback and you get the ball at the 20. In neither rule does it allow you to gain possession at the opponent's 1, so either the poster has his facts wrong or it's a glitch. And having blocked punts before in Madden, I do know that it does score his situation as a safety.
EDIT!
I'm not saying the poster has his facts screwed up (had to clarify there). I think it's a glitch not seen in previous Madden games.