Every click can also bring a searcher closer to a conclusion.
For example, when searching for a product you might visit the top site, find what you're looking for but then return to the results to see if anyone else sells it cheaper. Each subsequent click may confirm the top site offered the best deal so you spend less and less time on the lower placed sites and eventually return to the top one and place your order. If most people found the same thing the top site would remain top based on merit (user stats) - more time spent on site initially, plus visitor returned and placed an order.
However, most people might discover the best deal is on the 5th placed site, in which case the user stats would favour that site over time and eventually I would expect that site to rise to the top. User stats (Google's and each sites') indicate which site ultimately satisfied the searcher's query best, and the one that does the best job consistently will rise to the top and remain there (in my opinion).
The best site might not be the one that offers the best deal however. It may be the one that people trust most. Some people will go for price, some will go for trust, some will go for a balance of best price and a certain level of trust. It's the one most people lean towards that will eventually rank best though I think.
Google looks at the whole picture though, not just one statistic, but I do believe user stats are THE most important factor these days.