Lets see, we're 2 or 3 years ahead of next gen, you can't make that assumption just yet. Let's compare the PS4 to the Xbox 360 which had a wonderful start to this gen.
Look at Microsoft. All they had pre-X360 was Halo. That was their only big game. Then look at the 360, they released a 6-million seller (Gears) in their first year. Then in the 2nd year, they had a few 2-million sellers (Mass Effect, Bioshock, Dead Rising). Forza 2 sold around 4 mil and Halo grew to 11 mill. They also had some pretty superior multiplats like AC1 and MW1. Note that many of the 360's early exclusives went multiplat.
Now let's look at the PS4. It has a 5/6-million franchise (Uncharted). It has a 10 million franchise (Gran Turismo). It has another 5-million franchise (God of War). It has a 3/4 million franchise (LittleBigPlanet). It has numerous 2-million franchises (Killzone, inFamous, Resistance, Heavy Rain). Note that these games will never go multiplat.
We also have future titles which could be mega franchises on the PS4 (Twisted Metal, Starhawk). Who knows, maybe AGENT will be super successful and have a sequel on the PS4.
You seem to forget the importance of New IPs. This is probably the most important factor. Some of the biggest franchises this gen are new IP's like Assassin's Creed, Gears, Uncharted, etc. No one knows if one of sony's dev makes a mega franchise. Look at how ND went from Jak to Uncharted, or Sly to inFamous, etc. Who knows, SONY Could buy a new studio which racks in millions.
And the biggest game COD wasn't that big last gen. No one expected COD to be as big as it is. No one knows if one of Sony's IPs grows to be mega huge. Look how much bigger God of War got this gen. Look at how much bigger Killzone got this gen.
So yeah, no one knows what IP's will be created next gen or what franchises will blow up next gen.







