Oh because you know what the 720 specs are.

Actually it's just a matter of piecing together the puzzle if you know a decent amount about tech.

So to start, Wii-U as been mentioned many times to be using Power7, Something IGN took into account when building their own Wii-U from the specs developers had mentioned.

This leaves MS/Sony with a choice of matching the Power7 or stepping up to a Power8, While Power8 is a possibility its also unlikely since keeping the launch price down is going to be a priority, The worlds economic state makes this a given.

Then for GPU, it has been said by a few sources now that both Sony and MS will be going to AMD (Pity, I wanted PhysX) and sources have also started to surface about which GPU will be the choice of which system. With the new GPU's of this year rolling out now, we get a good grasp of what is likely to appear. Now for instance we will not be getting a top of the line card in either system if AMD is their choice. The operating temperatures of their top of the line models are extremely high, And require a lot of cooling, Something consoles can't really offer. So they will be picking something with a good balance of power/temperature and even Wattage, all of these are going to be a factor in the choice, It will be a Mid-High range card, certainly not top of the line.

Although my personal suspicion would be that MS will also use the 7 series GPU, As they certainly still have enough spare time to change their mind if Sony do go ahead with the 7 series. However sticking by the 6 series would still provide very close specs while also providing the Nextbox with a slightly lower price point.

This gives you the gist of where things will go, but of course an outsider is not the one calling the shots, so you can only really narrow it down so much

Well there is Power7(2010), Power7+(2012), and Power8(2013-2014). While Power8 might be more expensive, its cost will be less than $25 bucks for production. Everyone complains about costs, but major factor in PS3 cost was Blu-Ray. They can throw every bit of CPU/GPU tech in a console for less than $600 bucks and sell at a small loss and gain all of that cash back before the generation is over. PS3 cost about 900-1000 bucks for production. Without Blu-Ray it would have cost about $525 bucks similar to X360.

Its not hard to guess the specs. Power7+ is most likely. From what has been rumored. Which is 32nm and Power7. Power7 only exists as 45nm. Power7+ is the 32nm version. Power8 is 22nm.

From what I have read in rumors its alined with 6 core version, but 8 core could easily be in the system with 32 threads and 6 core as a early kit test run. Its also possible that Power8 could be in the system. Its coming in 2013. Would be vastly superior to Power7 tech. Would not represent a great change design/programming side of things. So it would be easy transition from Power7 to Power8.