From what I understand, Microsoft will only allow a peripheral maker to put a 3rd party controller on the Xbox if it has the Xbox standard buttons in place; along with the xbox guide button. And I believe Sony are doing something similar on the PS4 for full system wide compatibility. Even though game devs can add support on their PS4 games for any device they wish.
But when you take into account the licensing fee Logitech has probably had to pay to put a wheel on the X1, that is most likely where the price increase has come from. Obviously there is no point in Logitech putting a wheel on the Xbox, if they have to sell at a potential loss right out the gate. I am sure the price will drop relatively quickly though.
Still, when you add up how much the full Thrustmaster setup will cost for the xbox one; the new logitech wheel does make some sense. Obviously it doesn't come with the shifter, but it has slightly improved G27 pedals in the box. The shifter should be around £50 to £60.
Either way, it is no bad thing in my opinion for Logitech to have a wheel on the X1; and I am contemplating paying up for the new wheel. If it is anything like the DFGT, G25 and G27; it will have damn near bullet proof reliability. Worth paying the £300 for in my opinion, as it will still be cheaper than the Thrustmaster TX, T3PA (or T3PA Pro) pedal set, and TH8A shifter.