There's an entire class of professionals out there these days who don't use laptops. It's possible to run quite a sophisticated business entirely from a phone these days, and a lot of people who are doing exactly that.
Sure, there are professions for which this doesn't work - but even as a software engineer I find myself increasingly frustrated when I can't do things like review a simple pull request on my phone if I'm away from my desk rather than pulling out my laptop.
In 2012 sure, but with so much professional work being done asynchronously and mobile phones/browsers being so capable now mobile availability is table stakes.
A few features may be disabled, but if I log in and see a messed up layout or a "please log in from your desktop" screen it's a big red flag for quality/execution shortcomings that will bite me on desktop soon enough.
So I only have to build for laptop sizes and up. For what I do, anyway.
Not many applications are intended to be used on both.
In particular I think most applications for professionals assume you are on a normal computer, not a phone. Consumers, OK.