Apple get away with it fine in iOS. Unless MS are alleged to use their position in desktop computing unfairly they are fine.
Note that MS don't have anywhere near a monopoly on browsing on Windows anymore, which surely puts them in a safer position against claims they are using their IE-desktop dominance unethically.
It'sa closed platform, there is nothing illegal with that. Closed systems have been around forever... games consoles don't even let you install software on them that's not approved centrally (without some messing about).