Implementing a "remove from my list"-button will cost time (thinking about each and every scenario), developer resources (someone needs not only to implement the button, but also the API and the backend modifications), and a lot of other resources. The return
of investment will not be measurable - nobody will switch from Apple to Microsoft because you now can remove an app from your list. Indirect and long term consequences are often hard to measure - it's easy to see how frustrated someone is when iTunes deletes
his local files on purpose (see here), but you need time to test for the effect of not being able to clean up your purchase history. Also this problem only effects a minor group of users.
What currently is not understood by Microsoft is: they do have a diverse user basis and they need to deal with about 100 problems covering 1% of the user basis each. So when they ignore all the 1%-issues, they will make 100% of the customers angry. With
a user basis like "all windows users", you need to fix ALL annoying issues - and in my opinion this is an issue that does not cost too much to fix.
So @Microsoft: simply implement two buttons: "hide this item" and "show hidden items" - that would fix the problem for me completely.