I was actually called by my sons nursery once. I sent him in with what I thought was just a cold, and they phoned me and said he had 38.5 in temperature, could I please pick him up. I live nearby so was there within 20 minutes, and he was a sorry sight, so straight to the GP.
My boy has a respiratory condition (not asthma, yet), and when he gets a cold he may often sound horrible, and he needs inhalers to open his airways, as his larynx tightens. A cold for him may very easily turn into a Chest infection, or his larynx may just flatten and he cant breathe.
Bossy, I think many has the same opinion as you mention, "I pay for this nursery place, it is damned expensive, I will get my moneys worth so shall not keep the child home".
As for it being an old wives tale to wrap up warm to avoid colds? Not at all, my gp explained to me that being cold does not give you a cold, but if you are cold, your body's immune system is weakend, so if you have the virus, it WILL break out if you are cold.