They might be heavier users. If I had to guess, I'd say road warriors (people who do a lot of traveling on business) tend to buy Iphones, which is why the usage is so lopsidedly heavy on the Ios platform. Apple might have a cool factor, so sales people feel they look better using one. Maybe the ergonomics are superior, so heavy users, like people who do a lot of travel, prefer it. Or it might simply be first mover advantage - the first people who bought pricey Iphones were the people who needed it (again, frequent travelers), and they've stuck with it just because they're familiar with it.
The answer is ... very simply ... the iPhone is very much easier to use with these services and is more of a joy to use, which prompts more usage.
These are not road warriors, but ordinary people, and grandmas and grandpas (and I know quite a few of those using iPhones) ... using their iPhones and doing ordinary and everyday things in and around their homes and shopping and communicating — in other words ... doing very, very “ordinary” things.