The PlayStation Store is a part of the PlayStation Network where both PlayStation 3 and PlayStation Portable gamers can purchase downloadable content like games and accessories for their PlayStation Homes. Currently, customers can play the games they already own (even if the game requires online access) but cannot purchase new content through the Store. The fact that PSN Sign-in is still offline due to "maintenance" does not impede users' access to their games.
Not only have customers been locked out of their PSN for almost an entire month, gamer developers and publishers have also suffered from delayed launches and lost revenues from those delays. As a result, Sony is planning to push out two games per week to help its partners catch up to the original publishing schedule, as outlined in the memo.
According to Gamasutra, "The launch of the PlayStation Store is one of the final steps to bringing the PlayStation Network back to full operation. Sony has said many times that it expected the network to be fully operational before the end of May." Plus, until the Store is back online, customers cannot download the games and content that is part of their "Welcome Back Package".
Hopefully this last piece of the puzzle will be relaunched as scheduled, without any more hiccups.