Samsung phones are very often dinged in reviews because they ship a confusing mix of Samsung apps that duplicate the functionality of Google apps. I wouldn't be very surprised at all if Samsung would prefer to just ship their Calendar/whatever app, or even entire phones that only contain their apps/services, but they can't make those choices.

Regarding the 75%, please bear in mind that that is across the total market, which covers a very broad range of price points. Apple may have ~25% share, but that is skewed almost entirely to the top end of the market. In the low end of the market, Android would be nearly 100%.