I have read the official response from Facebook on this statement (which is that "clicks" is clicks that's not part of the result, e.g. going to a page instead of liking it) But it still puzzles me, when I run an ad with "Clicks to Website" as target, how can clicks on the ad NOT give a result? No matter where you click on the ad, you will be taken to the website. So what is this? Because I spend a lot of money on these "clicks" 
The ads manager says:
Clicks have always included actions. Since the dawn of ads on FB. This is why people often find page/sponsored story ads don't do as well as they would like because they pay both for clicks to the page they want and for likes/shares etc.
You are not paying for "Clicks to Website". You are optimising toward "Clicks to Website".
Aha, I misunderstood. Actually - checking my stats - "Clicks to Website" and "Clicks" always equals the same number when optimizing for clicks to website. I thought that I paid for "clicks" that were not "clicks to website" when doing this. Thanks zeno & cmdeal
This is common. You should always optimize your campaigns around click to website cost instead of FB's regular CPC. Sometimes clicks to website are anywhere from 15-30% more expensive than what you're actually paying. The easiest way to measure is just look at your clicks to website cost on FB and then look at your advertorial/presell's RPC (revenue per click). Can't get any more basic than that 