Speaking to Nikkei Japan, SCEJ's Masayuki Chatani said,"We would face difficulties if our business depended solely on the sell-and-forget model. After we sell the hardware, though, we continue to sell products such as content and services.
"We can also accept payment in a growing number of ways. In addition to single-payment packaged software, there are also schemes like monthly fees or per-item charges."
Before you fanboys start grabbing the pitchforks, note that Mr. Chatani was only speaking about specific titles during this little schpeel, and not the PSN as whole. Even Kaz Hirai stated that current services would be offered free of charge.
However, there have been persistent rumours that Sony is considering some sort of subscription model, but whether this is for individual games, premium content, or the Network as a whole is something that remains to be seen.