I don't get how people are saying Apple is anti-competitive in this case when Amazon has a huge closed platform themselves called.. 'Kindle' e-book reader. it has many more units out there than there are iPads.
Can Apple sell iBooks on Kindle without paying Amazon *at least* 30% comission (or 70% on many markets)? No.
Is there an option to install an Apple store on the Kindle? No.
Maybe the anti competition authorities some commenters have in mind could look into this problem.
If a company (eg, Better Place) started to create its own network of battery changing stations to sell its own electric cars, it would not be required to change batteries on cars from other manufacturers. But if an existing network of battery exchange stations (with lots of customers and being the de facto monopoly) started to manufacture cars and then would charge other cars 30% more (with these other cars having no alternative to change batteries), it could be in trouble.
In the end it all comes down to defining markets. If you cannot easily separate two parts of a business, you cannot force it to separate. Take you electricity: often production and distribution is handled by the same company which naturally has no interest in letting other companies sell electricity in their region. But you can separate the two and enforce competition.
So, anti-anticompetion action requires:
1) an existing or easily imaginable market (ebooks on iOS, ebook stores on Kindle hardware, battery change service)
2) a dominant market position (eg, Apple with tablets, Amazon with Kindle books on the Kindle hardware, battery exchange stations)
3) abusive behaviour
So, yes, ebook stores on Kindle hardware is an imaginable market (similar to distribution of electricity as a separate entity was while production and distribution were still integrated) but it clearly is not an existing one yet (as third-party apps on the iPad clearly is already). It is much harder to define the viability of a non-existing market and to define and prove abusive behaviour in a non-existing market (you cannot prove electricity companies overcharge customers for the production of electricity unless you have forced them to open their distribution to others). Usually this kind of market opening (or rather market creation) requires some political push to get going (though sometimes a legal complaint can also kickstart this).
As I said before, to postulate market domination you first have to define a market and all competition law requires that adjacent markets are considered. Thus ebooks on Kindle hardware has as adjacent market actual physical e-ink e-readers (Nook, Sony and others). And including this adjacent market, the ebook store Kindle might not be that dominant anymore. The same can be said for the Kindle app on iOS, of course the Kindle software on the Kindle hardware is an adjacent market. And for the battery changing stations the market could be defined as providing vehicles with energy. And unless a large proportion of that energy would be provided by those stations (and not by petrol, hydrogen, or charging), they might not be considered to dominate that market.