pawsplay
Hero
I think the closest book that fits my description of “perfect” would be the D&D Rules Cyclopedia.
...Just to be clear: by all-in-one I mean the only core book needed by both GM and player is just the one book. In fact there are no other rule books for the system. GM’s might use modules, depending on the GM, but I don’t consider them a core item.
The OP is kind of confusing. As far as I am concerned, the Rules Cyclopedia is a nearly perfect game-in-one-book. That doesn't mean it's the best game ever, or even a particularly good one, only that the design goals were solidly fulfilled cover-to-cover. The RC is very nearly the best of of all possible RCs.
Many games do not succeed at this. Despite its size, Hero System 5e is very nearly complete, but does not contain nearly enough pre-statted animals to handle even the most basic Western or dungeon crawl. How strong is a horse? You'll have to buy the bestiary to find out. Warhammer FRP 2e and Star Wars Saga Edition have nearly crucial expansion materials outside the main book. Et cetera. On the other hand, Blood of Heroes contains the entire DC Heroes 3e system, numerous pre-statted adversaries, and even a version of the chart you need for play. Unfortunately, instead of fully statted DC Heroes, you get a bunch of horribly designed weirdoes from the designers' home campaigns. It's an ugly and poorly realized supherhero book.
The realy complete and well produced books I can think of:
Rules Cyclopedia (king of all single-book systems)
Talislanta, 2e
Mutants & Masterminds, 2e
Warhammer FRP, 1e
Star Wars, Second Edition Revised (WEG)
Shadowrun, 4e
The Dying Earth RPG