Microsoft and Xbox are hardly a monopoly. In context, Xbox is Steam, PSN is GOG, Nintendo might be....i don't even know. You see my point. MS has a monopoly on Xbox but that's like saying you have a monopoly on your house, it's hardly a bad thing. Customers can always choose to buy from Sony, or Steam etc. If it's an exclusive game that's a different story.
Anyway, the truly ridiculous situation where physical is CHEAPER than digital during a sale no less is most likely either a mistake or some silly attempt to push you to buy digital. You either play along or refuse to pay. I am still holding off on Forza 5 even though i really want it. It's still $60 digital though i'm sure sales are no longer super hot, and that it could do with going to $40.
Both Microsoft (Xbox) and Sony (PlayStation) have a monopoly over their own stores, neither is like steam which is in an open market-place (PC). Not sure how you came to the owning your own house monopoly conclusion, a better example would be if you owned every rental property in the US/UK/Aus/etc and dictated the rental prices. (That's a monopoly)
I'm also not sure how having a more expensive digital copy is an attempt to push you to buy digital. If they wanted to push digital they really should be making it cheaper.. Or atleast cheaper than physical which acquires additional costs due to the casing, disc, booklet and shipping costs yet it somehow manages to cost less than digital.