As discussed in APS-C Emerges as “the new full frame quality”, there ought to be format-equivalent apertures with lenses: f/1.0 for APS-C (equivalent to f/1.4 on full frame), and f/0.7 for Micro Four Thirds (M4/3).
Why do the smaller formats not have such lenses (with a few not so enticing exceptions)? Perhaps because the smaller formats are not yet deemed a serious market in which buyers would pay big bucks for a fast and well corrected lens. This might change in time.
In the meantime, one can shoot the Leica 50mm f/0.95 Noctilux on Sony NEX, but it doesn’t really deliver the same effect: for the same field of view, one has to be considerably further from the subject. No, what is needed is f/0.71 for an APS-C camera.
Below are two images from the Wide Aperture Landscapes page in Guide to Leica, on full frame. Full-frame is hard to beat for the rendering style, just as large format has its own classic look compared to 35mm or medium format.