Others can do it because they don't have a monopoly. Windows still must be distributed without its media player in Europe.
And Apple already tried to abuse its position with the Kindle app by forcing a distribution commission for books it didn't sell. Also a guaranteed lowest sales price. They've hardly been kind to competition on their platform.
"""And Apple already tried to abuse its position with the Kindle app by forcing a distribution commission for books it didn't sell."""
Well, regarding Apple forcing Amazon to play a distribution commissions for books sold through the iPad, it was either that, or allowing other companies a free ride to sell on Apple's platform, the Apple spend tons of R&D on, without Apple getting anything.
Apple puts those restrictions because it considers not just the hardware of the iPhone, but also the App Store as a platform that it have invested money, engineering and infrastructure in, and wants to profit from it too. Apple doesn't believe in the old mantra "apple only makes profit from the hardware". With multi-billion app/song/book/etc sales, why should they?
Allowing others to sell stuff in your platform without paying you makes sense if your platform is an operating system.
It does not make sense if your platform is an application market.
Now, regarding "being kind to competition on their platform", indeed they have been not. But they would have been foolish to be. They invest in building a game changing phone device, then a game changing app store AND a game changing mobile platform, why would they invite competition in their own platform? Let competition exist between multiple platforms.
And Apple already tried to abuse its position with the Kindle app by forcing a distribution commission for books it didn't sell. Also a guaranteed lowest sales price. They've hardly been kind to competition on their platform.