Silly Domains

One thing that has always bothered me is the determination of domains in rational expressions before they are simplified. It does not make sense to me and I have not had a logical explanation from anyone yet as to why it is done the way it is done.

So the domain of ((x+6)(x+4))/((x+2)(v+4)) excludes x=-2 and x=-4. But it could just include x=-2 if it were simplified first. Go figure.