I don't think they'll be able to sell 150 million units again. The only platform to ever come close to what the PS2 did was the DS, which Sony obviously had no involvement in.
The PS4 has been quite impressive, selling 1 million units in only 24 hours (Which is a record, last I checked), but what if it doesn't have as many reasons to be bought as the PS2 did? Could that have been a once-in-a-lifetime accomplishment for Sony? It looks like it to me.