It's a bad habit, but it's pretty common. Really, there's two distinct things to consider when building responsive design. One is viewport size (and really just

It's a bad habit, but it's pretty common. Really, there's two distinct things to consider when building responsive design. One is viewport size (and really just width in most cases) and the other is touch vs mouse. Vertical monitors is one case, but so is touch-enabled monitors or mouse-enabled handhelds. Most of those are considered small enough edge cases, that it's not worth investing. Most websites look kinda crummy if you use a phone in landscape too. I used to insist that designers never say "phone, tablet, desktop" and instead say "small, medium and large" but it never stuck.