You already know the what the launch games are for the PS4?
No, but what games could they possibly have? For the PS3 they had Resistance, and for the Vita they had Uncharted. Both are western games that barely made a blip on the sales charts. Most of the big franchises for Japan have moved to handhelds. Sony certainty doesn't have any big first-party sellers for Japan anymore and there's almost no chance GT6 will be a launch title. FF will not show up for at least a few years, if at all. Can you even think of a 3rd-party title that sold 100k+ first week alongside a console launch, ever? Or do people here not remember waiting months for Virtua Fighter 5, which sold a paltry 48k first week, the best performing PS3 game at the time by far?
Why would the WiiU be selling better than the PS3/PS4? Which games has Nintendo announced for that time period? (although it's just 5k)
Why is the PS4 going to perform worse than the PS3 has been doing? You'll have to look at different things like launch games and price, do you really think Sony is that stupid to pull another 599$?
I'm throwing out guesses, but the PS3 has been declining YOY for a couple of years now, and with no big software on the horizon (except vaporware aka Versus), a more saturated market, and more competition with the PS4, that will only continue. As for why the PS4 will sell less than the PS3 / WiiU, just look at the previous two Sony game systems. The PS2 continued to outsell the PS3 for at least a year after it came out, and here in 2013 we still have the PSP outselling the Vita. Again, the PS4 will likely have little compelling software at launch, just like the PS3 and Vita did. I'm not saying this will definitely happen, but I wouldn't be surprised if it does.
If the rumors of a fall 2013 release for the PS4 are true then those PS4 numbers are HORRIBLE, it's impossible for them to accomplish this.
If I were to tell people back in 2011 that the PSP successor would be struggling to sell 10k or back in 2009 that the Wii successor would be selling 20k barely a month after launch, I probably would have gotten similar comments. I hope I'm wrong, because I would love to see the PS4 do well in Japan. I'm simply looking at past trends and trying to draw reasonable conclusions.