On m43 as the mirror is not required the flange focal distance is much shorter, so by having an adapter, it's possible to adapt many manual lenses out there. The thickness of the adapter will satisfy the FFD requirements. Whereas for DSLR the FFD is longer, you can't adapter lenses which distance are shorter than it, it will become a macro lens instead. E.g. if you look at wikipedia , you can put leica m-mount, contax g lenses and even c-mounts on m43 (20mm FFD), however, not on say Canon EF mount. The same goes for other mirrorless camera (Nex, NX etc)
Another point, I was using Oly 43 E410 dslr b4, the viewfinder is small (smaller than most DSLR), manual focusing is a big challenge, with EVF, it possible to magnify but really the VF2 is good enough mostly even without magnification. If you plan to use manual focus lenses, it's better to go with VF2. Was just trying an Canon 50D with a manual lens to try manual focus, it was difficult with the optic viewfinder, not that it can't be done, it's just difficult for me.
Hope that helps.
