That's not, in itself, an argument against calling soldiers heroes. All it does is establish a certain degree of parity -- perhaps we need to treat our mailmen better. However, this next argument does seem to tell against the rhetoric.
Heroes are, by definition, people who do extraordinary things, usually extraordinarily courageous things. If soldiers are heroes, then, we would expect them to be able to do extraordinary things. But, soldiers very often cannot do extraordinary things. While they may be exceptionally well-trained and -equipped (in an ideal world, anyway), there is nothing necessarily exceptional about the soldier him or herself that qualifies the soldier as capable of the extraordinary. (Indeed, since it seems that most soldiers are not well-trained or -equipped for the tasks they are actually assigned -- witness Iraq or Vietnam -- they are very often not even capable of the ordinary -- witness Haditha and My Lai.) So, there is a factual error involved in calling soldiers "heroes". Moreover, there is a great danger involved in calling soldiers "heroes", in that they may be expected to perform tasks they are not trained or equipped to perform.
On the whole, then, perhaps it is time to recognize soldiers for what they actually are: namely, ordinary people doing a dangerous but necessary job, who must be given the skills and equipment they need in order to fulfill the purposes of that job. (Just like the mailman.)