It's a good suggestion, and would add some nifty detail to plants, which I'm all in favor of. However...
Most of the time one seed won't work. You'll need at least a dozen to be sure. That's why strawberries and the like have more then one, to improve the odds.
And how many times have you done that? It's inconvenient and you'd be left with half a strawberry since you would inevitably take out a good chunk of fruit.
All the seeds on a strawberry are on the surface, right? Just take a knife and slice off the skin on one or two sides, and you'll easily have dozens of seeds.
The really problematic berries would be the ones with soft internal seeds. You'd have to be pretty desperate to pick the seeds out of all your blueberries and "seedless" grapes at the dinner table and still eat the remains.
I think a better idea of how seed collection works in DF is that it's a function of every fortress's omnipresent command economy: Dwarves eat a bowl full of (magically supernourishing...) blueberries in one sitting, and save five percent of their blueberry ration for seed purposes, since the bureaucrats didn't think to save a handful of berries at the point of harvest instead.
Of course! It's actually a social engineering policy. It was clearly designed to enhance the morale of the proletariat by giving peasants the illusion that everyone helps farm for food, even the factory workers.