You tend to see drug tests a lot in retail, fast food, and many other low-wage low-skill jobs. I truthfully have no idea how effective that is in weeding out people who would be generally unreliable, but that's often the justification given by managers.
I'm sure there are some ultraconservative companies that drug test everyone — including developers and senior managers — but those are few and far between in comparison.
Unfortunately, drug tests are yet another hurdle poor people have to clear in order to earn a living wage.
Outside of the red tape domains, like banking and government, I've never been drug tested as a developer. The idea that a low skill worker is more likely to be on drugs is classism. Low skill workers really get no autonomy. They are drug tested, have to clock in and out, and even have monitored lunch/bathroom breaks. It's kind of disgusting to think about.
There certainly is some of that, but there's also different requirements for customer service positions where being in a specific place at a specific time is a core part of the job.
There's at least a few places out there run by Mormons who do hair-tests on their employees and won't hire you if you've been drinking alcohol. Even for high-level managers, executives and the like. (Enough of them that I've run into one person talking about her employer doing that, anyway.)
I work at a large telecom company and we drug test everybody.
Incidentally, it's quite awkward if you're currently employed when you get the new offer - as I was. The lab that collected the urine sample opened early in the morning for "regular" work but only accepted drug test samples from 10 AM to 3 PM on weekdays.
I'm sure there are some ultraconservative companies that drug test everyone — including developers and senior managers — but those are few and far between in comparison.