Despite political wrangling over the meaning of "Intelligence", most people outside of academia have a pretty good common consensus of what that means. Wisdom is hard to quantify, but it is another thing that "I know it when I see it". The whole 'getting better at seeing as you get older' is a quirk unique to d20, not to the ability score system, since it predates Spot and Listen skills by a quarter century.
One of the reasons that D&D has so successful, and that its format has been so copied by other games, is that those basic six ability scores are a good shorthand for describing a persons talents, strengths and weakenesses.
Yes, if you wrote down a rigorously tested, scientifically evaluated list of a persons strengths, weaknesses, potentials, aptitudes, weaknesses, deficiencies, and talents you would get something a lot bigger than a D&D character sheet, and a lot less comprehensible. However, those six figures between 3 to 18, with 10 being average, is a nice shorthand for approximating how to describe someone (real or fictitious). If it was so deeply flawed, I doubt so many people would have the attachment to the 6 ability scored that they do.