Except in order for that game to be in a GameStop, Walmart, or KMart, the developer of the game has to sign a publisher agreement with Microsoft. This agreement gives Microsoft a royalty for every copy sold, plus approval rights over the final game, marketing, and packaging materials.
So, no, a developer cannot distribute a game for Xbox without Microsoft's approval.
This is also largely irrelevant to the question of whether the market of "games for Xbox" is a separate market from "games for Nintendo" or whether they're actually both competitors in the "video game" market.
So, no, a developer cannot distribute a game for Xbox without Microsoft's approval.
This is also largely irrelevant to the question of whether the market of "games for Xbox" is a separate market from "games for Nintendo" or whether they're actually both competitors in the "video game" market.