You must have Microsoft's approval and pay them a cut before your software will work on their console, physical disk or not.
Exactly as is the case with iOS, Nintendo, or PlayStation.
Exactly as is the case with iOS, Nintendo, or PlayStation.
What this boils down to is, what my options are when selling my game. On Xbox, Nintendo Switch and PlayStation I have choice over how I sell my game and can choose different avenues that have different pros and cons (More sales with Amazon, but less profit per copy sold vs. More profit per copy, but less sales when sold direct). With iOS you don't have that choice, hence they are a single buyer.