The Iris Pro HD 5200 is only found in specific quad core Intel Core i7 CPUs therefore the CPUs will be expensive. Additionally, it requires eDRAM which must be installed on the motherboard; this adds even more cost to the laptop. BTW, the Iris Pro HD consumes too much power to be considered for ultrabooks. The Intel HD 5000 graphics core is found in some ultrabooks, but it's performance is no where near the Intel Iris Pro HD 5200. It's performance is in between the Intel HD 4400 and the HD 4600.
Would I like to have a laptop with an integrated HD graphics solution that has about 85% the performance of a nVidia GT 750m? Sure. But I would also do not want to spend too much money for a laptop that is not a gaming laptop. There is more or less a niche market for the Intel Iris Pro HD 5200.
I think the i7-4750HQ is the lowest end CPU that has the Iris Pro HD 5200 option (assuming eDRAM is installed on the motherboard). Intel lists the tray price (meaning a lot of 1,000 CPUs) at $454. Therefore, it is not going to be in any affordable laptop.
People who usually spend a lot of money on a Windows laptop are people looking to buy a gaming laptop or a graphics workstation. Sure people can use the Iris Pro HD 5200 to play games, but I am pretty sure they would rather get a dedicated graphics chip / card. Sure it can be used for graphic design programs, but serious designers want support for dedicated workstation class graphic chips / cards and driver support. The Intel Iris Pro HD 5200 doesn't really fit into the two mentioned categories.