That ideal search engine would find itself quickly the target of people that would try to gain an advantage by figuring out how it works.
And then another SEO cycle would start. Don't forget that before google came along nobody was trying to 'game the system' with backlinks and other trickery, the fact that that google is successful is what caused people to start gaming google.
Any real-world search engine is going to be analyzed until enough of its internal mechanisms are laid bare to allow gaming to some extent.
Typically you pretend the search engine is a black box, you observe what goes in to it (web pages, links between them and queries) and you try to infer its internal operations based on what comes out (results ranked in order of what the engine considers to be important).
Careful analysis will then reveal to a greater or lesser extent which elements matter most to it and then the gaming will commence. Only by drastically changing the algorithm faster than the gamers can reverse-engineer the inner workings would a search engine be able to keep ahead but there are only so many ways in which you can realistically speaking build a search engine with present technology.
Your ideal, I'm afraid, is not going to be built any time soon, if you have any ideas on how to go about this then I'm all ears.
I think the solution is a diversity of search engines. Maybe even vertical search engines. These days I get such shitty results from google for programming related searches that I've started going straight to SO and searching there. If I don't find it there I then try google, then try google groups search.
