Main reason is due to upgraded SKU's over the years. But still, a great feat for all 3 companies, but especially MS.
At the end of last gen, you could buy all 3 main consoles for under £200. In way, it was great for MS to break the 360 into the market at launch when you could buy all 3 (PS2, XB, GC) consoles in good condition and a few games for the same price. as a non bundled 360, which ranged from £210 to £280.
I doub't the same will happen next gen. Around Q4 next year I think to buy a Wii, 360 or PS3 (good condition) will cost around £350.0
If the next console (not WiiU) releases at under £300, it will surely be a hit.