Anyone who is saying the PS4 won't do well in Japan is somehow missing the massive amount of exclusives-by-proxy the Playstation brand has over there. There are far too many to attempt to list.
Really, the only thing that will hold it back is the PS3, as Japanese developers are typically slow in jumping to the next generation. The PS3 will continue to sell software while the PS4 builds up a library. By the time developers have switched over to the PS4 full-time, the hardware will sell at a healthy rate.
Before anyone gets happy about the PS4 starting off slowly, this is not a Wii/Wii U situation where they kill off the predecessor. All the games will come to the PS4 eventually. It's just a matter of time. The PS4 will do well simply by virtue of having a massive amount of games.