I still don't think you understand. A 3D game cannot be made by someone who doesn't know these features. Developers don't have to know everything there is to know about an engine (even the engine's developers don't know that), but if they want to select the best engine for their project, they need to know about engine features. There are many sites they can use to learn (and after all, that's what it's all about), but they will need this knowledge if they are to usefully and productfully use their engine.
Why would a developer be looking for an engine similar to quake 3. Why not looking for one that as fast BSP rendering, is GPL has render-to-texture and texture mapping. They might not want it to be OpenGL, so they run a search for those features in DirectX. Rather than clicking Quake 3 and selecting "engines similar" which is never going to do justice to the diversity of engine fatures and intended purposes.
About apples and oranges. What do they have in common. They are fruit, they stimulate the taste buds that recieve sweet taste. Apart from that? Not a whole lot. Dissimiar? Oranges are round, oranges contain citric acid, orange skins are generally not regarded as edible, apple pips are brown, oranges are orange, whilst apples can vary in colour, a green apple may be ripe, whereas a green orange is unripe. I could go on a for a lot longer, but I hope you get my point. Also, I'm sorry to continue the analogy, but there you go.
Anyway, I think there is a place for your comparison and a place for the 3D Engine Database, I just don't think that place is together.