There are a couple things which led me to think all-mesh might be a drawback in harsher conditions (neither of which is really hard-data unfortunately).

First, in various forums and reviews I've stumbled across, I have found some personal opinions and anecdotes which put forward the idea. The most credible concern seem to deal with winds which can drive the cold and moisture, be it rain or snow, under the fly and through the mesh. Similar concerns exist around blowing sand or fine dirt, but that's less of a worry for me I think.

The second comes from tent manufactures themselves. If I recall correctly, MSR's now defunct HP version of the Hubba Hubba as well as their new Hoop tent are marketed as better extended season tents due, in part at least, to their fabric inner walls. Another example is the MEC Gemini I linked to above which is offered as an ES (extended season) model with fabric walls in addition to their original model which is mostly mesh.

Again, I don't really know if the all-mesh bodies are that big of a drawback (and I am still considering them), but this is what has led me towards thinking they could be a liability when its not nice out.