Why shouldn't you validate if a programmer is, in fact, a good programmer (which is a mix of many things, including intelligence)?
Programmers, however, must take a test. It's not an interview, it's a test. Pass or fail (regardless of what people say), it's a test. It's a test of which you have little preparation for. You hope that what they are looking for is what you can provide. What they are asking for is what they will test for (this is fairly often not the case).
Programmers are almost never asked to program. They are asked to solve 50-year old CS problems on a whiteboard.
It always comes down to exercises from CLR lightly dressed up.
Agreed. That would be bullshit. And those are bad interviewers if they do any of that. Companies like Microsoft, Google, Amazon, and Facebook don't do that, as a general rule. I'm sure you could find bad interviewers at any company though.
so yeah, ask me to program. i mean, srsly program. let's hack together for an afternoon; hell, let's do a full day of paired programming to knock out a small bug in your code base. you'll learn a hell of a lot more about what i know, how i communicate, steps i take when i do when i don't know something, and what my processes are. this soft, inter-engineer-social stuff is overlooked over far too often; i wan't to work with people who will amplify my process and abilities, and in turn i'll amplify theirs. smarts don't count for enough.
Comparing candidates is irrelevant. You just want N hires that can contribute in your environment.