Suppose there's a very popular keyword and a Google search results in eight sponsored listings being displayed to the right. The very first spot gets the best CTR. However, the very last spot also gets a pretty decent CTR since when people skim, they often read the first and read the last and miss the middle. Therefore, spot #8 might be just a tad bit lower CTR than spot #1 but a whole lot cheaper.
If you have a bunch of money and the CTR pays more than the cost of the CPC then I would not worry about it. if it is the otherway aroung you might want to be more targeted in the Keyword or pay less for it.
I'd say it's the cost. Especially if your visitors don't buy anything. You still have to pay for every click, right?
And also, maybe because people want alternatives. They don't usually buy what they first see. They'll want comparisons. And if they find that number 2 or three is just as good, then they'll stick with the latter, to save time and all.
Traffic may be one thing but in the case of paying for clicks wouldn't you be intereste dto know what the conversion rate of these clicks in position one two and three were as well. I think people naturally skip down the page for variety and comparison shopping purposes, although your studies are correct in what they hypothesise.
Well, for me, I don't buy the first thing I see. I can understand that position one and two is wonderful and you get hits, but for conversion sake I think it may be better to be a little down the line. The reason why I say this is because people like to shop around. Site #8 might have more detail than site #1 on a product or service and a little more detail on a product would get me to buy what is on the ad at #8 position. Do you know what I'm trying to say?
In pay per click I can see reasons due to cost. A first position may only have marginally higher or the same CTR than other positions in the top 5 but cost per click will be more.
For organic ranking there is nothing wrong in aiming for the top rank for your keywords. In practice top 5 rank should perform equally well. I cannot see any reason why a no1 spot will be worse off than any other position.