The four-thirds system is a much younger system than all of the other systems used for DSLRs, and is therefore relatively immature. It's much less standard than systems employed by the other manufacturers. I did omit that it has in-body image stabilization, but in my opinion it's a moot point since Olympus advantages are negated by the disabilities that its competitors simply don't have.
I simply don't get your point. People buying camera that doesn't have in body camera end up paying more for lens when they want image stabilizer in their new lens. So camera with in body IS can put any lens, even legacy one, and still have IS, so to me it is a big plus.
It's true that any of the DSLRs from the major manufacturers will produce better image. But conventional wisdom and the thoughts of critics and photographers would argue that one is better served by a selection from Canon, Nikon, or Pentax instead of the options offered by Olympus, Sony, Sigma and the other manufacturers. There is more room to grow, a healthier accessory ecosystem, and a much larger lens selection.
So you pick OSX over Windows because it has more accessories and software running on it or because what you want to do with it, it can do better. I chose 4/3rd because it's small and light and because Olympus is an innovative company like Apple. Company that lead with innovation for other to copy such as the Dust buster with no equal from other company as we speak. The first company to come out with live view etc, ect...I didn't chose Olympus despite what the so call critics said. Does "Think Different" remind you of anything? All my Olympus photogear I bough them used, so it's not that difficult for other to so the same.