The short answer is no.
There is an important trade off between shield and armor. Obviously shield upgrades affect more units (air and ground), but beyond that, shield regenerate so they often prevent damage more than once. By comparison units often have less shields than health. There is also a cost difference between the two.
edit: It is important to note that pro level Protoss players (ie. tester) often choose armor over shields. The reason for this, is that in a large battle, the higher amount of HP usually means that armor will have a large effect during the course of the battle, additionally, EMP dictates that Protoss are often less able to rely on their shields in TvP.