I don't want to go into the details of the case right now, but it is likely that the decision came a) from high up, i.e. Mubarak, and b) to avoid the embarrassment of having the administrative court rule in favor of Hizb Al Ghad and overturning the HPPC's decision. Note that the key decision-maker at that level is Safwat Al Sherif, the former Minister of Information and current head of the Shura Council and secretary-general of the ruling National Democratic Party. As you might guess, he's no fan of new parties.
The bottom line: a good first step, but one that probably would have come anyway through the judicial system. Will be more excited if Karamah and Al Wasat, for instance, get through and if currently frozen parties (such as the rather nasty left-Islamist Labor party and the ridiculous Ahrar party) are unfrozen.