This is valid point if the user is making a purchase. In that case, the user will likely need to be using a popular browser loaded with graphical features, with images, CSS, Javascript and cookies enabled. In practice, it would be impossible to make a purchase via web with only Host: and Connection: headers. (How many websites engaging in online commerce require neither images, Javascript nor cookies.) That said, there may be instances where web users are not engaging in commerce or other uses that require graphics, cookies and interactivity (submitting forms, etc.). It would seem futile to show ads to users who may not see them due to their client potentially not showing images or running Javascript.
Even without any features enabled and not sending any headers, fingerprinting would let the server track what pages you visit and when (even across websites).
There's not much they'd do with that information (as you say, while it's technically possible, no one cares enough to make an advertising system that works without JavaScript).
The main use case would probably be a primitive way to track which pages are visited in which order, how popular various links are, which paths people took to get to a specific page, etc. Normal tracking stuff which I don't personally have a problem with, but privacy activists often tend to.
