I'd even go as far as to say i'm disgusted with Microsoft for allowing this to happen.
MS didn't allow it, they decided it being a first party title. I doubt Turn10 was like hey, how can we screw our fans over for a few bucks?
I've read about this whole micro transaction fiasco with Forza and Dead Rising 3/Ryse and it is shitty, especially with Forza. Much less content than previous versions, $50 DLC car pack, laughable prices on their tokens that the whole pricing system on them is terribad (the lowest amount you buy gives you the best bang for your buck lol), and the fact they changed how earn cars in game (no more car prizes) and how long it takes to grind out getting a new nice car, you can tell it was all changed to heavily encourage buying their tokens.
Basically Forza 5, has the grind system of a Free 2 Play game while charging you full price for the game still.
It has become a big issue, I've seen a lot of articles on it and Turn 10 even made some announcement yesterday, which laughably pissed people off more because basically they were like, hey we heard you don't like our micro transactions and prices, so for this weekend we are doing 50% off the cost of those lol.