Switching between these orientations is easy enough; the sensors in every phone I've used detect rotation just fine. But if you're not rotating the phone intentionally, like if you're laying it down on its back or, heaven forbid, trying to use your phone while laying down on your side, you're basically screwed. Yes, I know there are ways to lock the screen in one of the drop-down or settings menus or with a witch's hex, but ugh man, seriously? Then you'd have to turn it off when you're done, and again, ugh. It's easier just to sit up, which is the worst thing ever.
"This is some serious bullshit right here."
And there's another thing which happens occasionally. I sometimes get in a situation where I'm trying to look at a picture that's rotated 90 degrees from they way it should be, like the phone doesn't know which end of it is down. Rotating the phone, like one might do with any other object in the world, just causes the phone to change orientation, which causes me to twist it again, and so on, and eventually my wrist just snaps off.