Trying to Choose New Camera and Lenses: Sony NEX vs Olympus OM-D

The introduction of a 3:2 ratio for the frame was intoduced by Leica when they made their first cameras, based on a film frame. This new 35mm motion picture film was considered a smaller, cropped image format at the time, and people considered it unproffessional with poor DR and limited depth of field control (funnily enough, the exact same arguments against micro four thirds or smaller sensored cameras like the rx100 or nikon mirrorless).
If you look at pro cameras like the Phase One or the Hasselblads, you get a 4:3rds ratio. The Leica S2 is 3:2.

Most large format and medium format cameras are a 4:3 ratio (or 1 to 1).

There is less clipping for printing on 8x10 with a four thirds camera vs a 3:2 ratio. 
Regardless, a matter of taste, but to call 3:2 a traditional protographic ratio is true, but only for non proffessional cameras.

Generally speaking over the past 50 years, a studio or a working pro would have used a 4:3 ratio more than a 3:2.