DxOMark Lens tests are often flawed beyond being marginally useful.
Their M43 are performed with a camera that is by most accounts the worst Micro 43 ever made. This is true for the Sigma DN 30 M43 review.
It actually gets rather comical if you look a bit closer. As anyone who's read a bit about m43 knows, the Olympus 75mm 1.8 seems to receive nothing but lavish praise, both in terms of image quality and as an elegant piece of engineering (to these eyes, at least, it's about as attractive as a lens gets). DxO acknowledges that it's the best m43 prime (for some reason they reviewed it based on its performance on a Panasonic body, where it scored 23 overall and 11 for sharpness, which I'll henceforth write as 23/11), but you can tell they've become a bit fed up with all the praise it receives and try to deflate the m43 enthusiasts' bubble:
"If you’re a convert to the smaller and lighter Micro Four Thirds cameras then the Olympus M.ZUIKO DIGITAL ED 75mm f/1.8 is excellent, but to put it into some context it’s not in the same league as other portrait lens and camera combinations. Take for example the Nikon 85mm f/1.8G mounted on a Nikon D3X lately reviewed." (The score of the Nikon 85 1.8G on the D3X is 35/17.)
All sorts of things popped into my mind on reading this, such as - Why wouldn't the highest scoring lens at DxO, on one of Nikon's best FF cameras, yield better results than even the best m43 combination? ("$500 lens on $7000 body beats $900 lens on $900 body shock horror!") Why aren't you comparing a 75 1.8 m43 lens to a Nikon prime with an equivalent focal length (150mm)? Why do you keep mentioning the high price of this Olympus lens (c. $900 w/out discounts) without telling us the price of equivalent lenses in other systems, let alone while suggesting by way of comparison equipment worth $7500? For that matter, why not invoke the much cheaper D800, where the 85mm 1.8G scores even higher?
And then I started rummaging around with some of their numbers, leaving aside the oddity of comparing an 85mm with a 150mm lens. What if you put the Olympus on the best m43 camera, the OM-D? Its score goes up to 27/13. Not as good as the D3X score for the Nikon lens, obviously, but what if we try that Nikon lens on a few other Nikon bodies? On a FF D4 it gets 33/14 (i.e. sharpness much the same as the Olympus combo), while on a D700 it gets 28/11, which is exactly the same score it gets on the D7000.
After all that, the "gotcha" end of the review seems a tad inflated, shall we say.