The problem people complain of most with single wall tents is not general stormworthiness (and certainly not a tendency to leak or inadequate protection against windblown rain), but rather the tendency for condensation to form on the inside of the tent surface in humid conditions. Ventilation can help prevent this, which is why good single wall designs always place a priority on ventilation (but of course if the outer air has 100% humidity then ventilation won't help much).
The condensation has two consequences: (1) if you brush up against inside of tent you get wet, and (2) in some cases if it's raining the pounding on outside of tent will jar free condensation on the inside that then "rains" on you.
Double wall tents can get condensation on inner wall of tent, too, but it occurs on the inside of the outer wall, so the inner wall shields you from it. If you're going to be using your tent in extremely wet and humid conditions you might prefer a tent with two walls, something like the TT Stratospire.