Not saying this as anti-Google, pro-Microsoft or pro/anti anyone, merely agreeing with you that the "% of {area|time|...} search" means absolutely nothing.
Especially in the context that matters for potential Bing customers, aka ads buyers: I don't care about how many search there are, I care about how many people can see my ad.
Of course no big search entity has any interest of giving those "real search" numbers, neither the front runner nor the underdog.