Apple does not have a monopoly in the smartphone market, but it does have a dominant position there and a monopoly in the tablet segment where it does the same thing.
No you're not. The definition of dominance in the EU is primarily that you're in a position to materially affect market pricing, which I think is actually pretty easy to demonstrate in Apple's case.
Overwhelming market share isn't required, and there are several cases that have found companies to be "dominant" where they had less than 50% market share in the EU.
(As a good demonstration of this Google's own competition law settlement on Android apps pre-installation in the EU. Google do not approach anything like having a monopoly market share in the EU either, but they still settled because they were going to lose.)
Is it? App Store prices have been a race to the bottom for years, yet it's clearly in Apple’s interests to keep the prices high, both to keep their revenue from the service as high as possible and to stimulate the app economy. If they had control over the market pricing, why did the race to the bottom happen and why haven't Apple stopped it?
If the argument is that they don't care about the revenue and they actually prefer the prices as low as possible to add value to their hardware devices, then why are Apple charging 30% and not 0%?
They still may be attached to marketing and partnership opportunities I believe, though - you might not be featured in the store if you charge iOS users more than android or web users, just like they will probably not advertise a new movie or album if Amazon is allowed to sell it for a lower price.