Those who have been a little late to the PlayStation Portable party and hoped to get their hands on Mega Man Powered Up by way of the PlayStation Network should probably start making other plans. According to Capcom's Vice President of Strategic Planning & Corporate Development, Christian Svensson:
There are techinical problems that neither we or Sony are able to get around. The game doesn't run properly when put in digital form. So it's physical only for the time being (hold onto those UMDs, they're gonna be valuable).
This is a most curious circumstance, as the Japanese version, Rockman Rockman, has been released as a downloadable title in its homeland with no apparent side-effects. With any luck, Capcom and Sony will find a way to overcome whatever mysterious hurdle prohibits them from making the game available for download in the West.
Hopefully, an alternative might someday be provided in a downloadable version for the PlayStation 3, Xbox 360, and maybe even WiiWare platforms. In the meantime, good luck hunting for those UMDs.
Source: Capcom Unity