Last year, Tim Cook said that 75% of all Macs sold are notebooks[1]. Not all Mac desktops come with a mouse. Of course, people can buy a mouse, be it for their desktop or notebook. Or they can buy a tablet, trackball or external trackpad.
For mouse use on the Mac to be the most used input method, over one third of Mac notebook users would have to permanently use a mouse instead of the built-in trackpad. You can go to any Starbucks, airport, or school to see that that is not the case.
Not sure that usage at a coffee shop or an airport is particularly useful. Like I've said, I regularly use a mouse as my primary choice over the trackpad. But if I was going out and about, I'd almost certainly not bother taking my mouse with me.
As I've said, I'm not saying that most Mac users do regularly use a mouse (although every single Mac user I've ever talked to about it at work regularly uses one). But to demonstrate whether it's true or not, laptop sales figures and anecdotal evidence based on people's habits at coffee shops isn't particularly compelling.
Of course, sold != in use. Another assertion, but in my experience, desktops have a much longer lifetime than laptops. I think 'most used' is a bit of a diversion, since that's almost certainly the keyboard.
It's also a good way to show that Mac users wear shoes while using Macs at all times: just visit any Starbucks, or airport or school, nobody's using Macs barefoot.
Did you happen to hear the term "selection bias" before?
For mouse use on the Mac to be the most used input method, over one third of Mac notebook users would have to permanently use a mouse instead of the built-in trackpad. You can go to any Starbucks, airport, or school to see that that is not the case.
[1] http://www.macworld.com/article/1167850/apple_revenue_profit...