"Well, if that box wont be 150W power hog like Xbox360 was, then even that "modest performance" is great thing when delivered under 50W."
-- You cannot get a powerful console with a total power envelope of 50W. If you care about power consumption, go play on a smartphone or a tablet. Even the Wii U uses up to 75W in total and right now it's debatable if it's overall graphics power is even superior to PS3/360. Thus, you can't have a next generation Xbox that uses only 50W of power. Further, your TV alone will use 200-500W of power. Who cares if the power consumption of the Xbox 720 is 50W or 200W. Games cost $60. Power consumption cost is laughably low compared to the cost of hardware and software to matter.
-- The original Xbox used more than 150W of power. The number is actually around 180W, with an idle of 150W http://www.gamespot.com/f...-gaming-xbox-360-6302664/
"And you omit to notice that consoles usually offer only single screen support up to FullHD (1080p) for which even HD7770 more than enough."
HD7770 is not enough to deliver next generation graphics or DX11 games at 60 fps at 1080P, unless you set everything to low or medium, which defeats the purpose of next generation games. They are going to need something much faster than HD7770. You are also looking at today's games only but this console is supposed to last another 6-8 years. HD7770 will be laughably slow to last that long. The GPUs in PS3/360 were mid-range at least, which would imply a level of HD7950 or at least HD7870 by November 2013 next year as constituting mid-range.
"OFC we shouldnt forget how games became optimized for consoles by applying some tweaks to level of details that should be processed."
Games became optimized for consoles due to resolution upscaling. Most games on current consoles run at very low resolutions with chugging framerates. Black Ops 2 runs at 880x720 on Xbox 360. Other games like Far Cry 3 drop to 20-22 fps. Most games look horrendous up close but since a lot of people play 6-10 feet away from their TV, they might not notice the pixelation.
"And yet you all forget that Xbox720 should comply with DX11.1 while we still didnt see any commercial game being published that has been developed with that API."
What's your point? DX11/11.1 games are going to be even more demanding that today's titles. DX11 brings extremely demanding features such as contact hardening soft shadows, global illumination/dynamic area lights, bokeh depth of field, or allows one to use compute shaders for accelerating super-sampling on textures. All these effects are more demanding, not less demanding. That's why to play most games with real DX11 effects incurs a full generation performance hit just to enable those graphical features.
"Considering above mentioned even "modest" HD7770 should serve well for a long time when optimized 1080p graphics comes into play."
Not it would not. You need to account for demanding DX11 effects, rendering games at real 1920x1080 resolution, higher resolution textures, next generation particle effects, tessellation and more advanced game engines beyond what we have today. HD7770 is only enough to serve current generation game engines like CryEngine 3.4 or Frostbite 2.0. Those are not true next generation game engines, especially Frostbite 2.0 looks current gen not next gen. Things like Unreal Engine 4.0 and true next generation engines will probably start arriving in 2014 and beyond and HD7770 will choke and once again developers would need to start using dirty tricks like downscaled resolution and low resolution textures.
A lot of people are saying the next gen consoles will be underwhelming though with a large focus on lower prices and making $ off the hardware unlike PS3/360 generation. We'll see but keep in mind HD7770 will be slower then the worst AMD HD8000 series by 2013. That is budget territory. HD7770 can already be found for $110-115 with rebates. I bet MS can negotiate a price of $40-50 for this kit. It will be even cheaper in 12 months. I think they can reasonable squeeze an HD7850.