Is that up to them though? Aren't browsers on iPhones only allowed to be wrappers around the built in safari engine? If that's still true extensions that interact with the web page it's self would probably be pretty limited.
I keep reading that not as the venue doesn't have enough space for everyone, but as the venue has banned certain people. I'm really hoping I'm wrong and it is a space issue.
In addition to the exclusives issue, the client and store were not particularly well made and were missing pretty standard features stuff like no shopping cart so if you wanted to buy multiple games at the same time you had to do them as separate purchases and stuff like wishlisting.
I remember Valve got quite a bit of dislike when they first introduced Steam as a requirement to play Counter Strike Source and HL2 (of course back then it was only for Valves own games).
It's more they are focused on running ASP and CLI apps on Linux, there is no official MS GUI library/framework for Linux which is one big thing missing from modern .net, there are a couple of thrid party ones like Avalonia however.
This seems like some kind of thing some company would try so they could have a trademarkable word for memes.