It seems to me you're confusing words of encouragement and empathy with an attitude of acceptance at lack of results.
I've had management who gives encouragement exactly as the author describes, and it does help with my own state of mind. It does not make me think I need to try less hard (if anything, the opposite), nor does it give me the impression that they think it's OK I haven't produced results yet - only that they know I'm working on it, and appreciate the effort I'm putting into it. And that my manager is approachable, which is critically important.
In my own role in managing others, I find a bit of empathy goes a lot further than silence when someone isn't . (And that makes it sound more cold than it is - it's not a conscious choice of 'apply empathy, encourage employee, get results', but rather 'hey, it sucks to be in that spot. employee should know that I understand that - even though I still expect results.')
edit: mismatch paren