The way I've thought about this is in terms of available attention and routine. I may spend more time staring at a computer monitor, but that time is spent on

The way I've thought about this is in terms of available attention and routine. I may spend more time staring at a computer monitor, but that time is spent on my work routine, where new tools and apps are added sporadically at best. My phone, on the other hand, is where I spend time in a less routine way. Much of this time is up for grabs and the way I spend it changes on a much shorter cycle. But, to your point about other domains, I think the obvious answer is that there are certainly myriad products that don't need to be mobile-first today, if mobile just doesn't tie into their users' primary workflow. But even most of those services (HipChat, say) can become far more powerful by adding mobile apps. GitHub would be silly as a mobile-only service, but there are plenty of cases where accessing from mobile could be valuable.