This may appear to be the case in retrospect, but in practice this certainly wasn't the case because it assumes that the other combatants in the war were practicing human wave tactics or something, when in reality such tactics were becoming increasingly rare by the time Overlord was underway; probably limited to Japan, China, and certain Russian divisions (such as penal battalions). Now, in retrospect it can appear this way based on casualty numbers, but the US Army fought in a relatively small part of the war.

Now, we do we know that can refute this? Well, there are some pretty good examples. The first and probably most famous is the Sherman tank, famously known as the 'Tommy Cooker'. This was a tank that was very capable in 1942, but by 1944 was outmatched by the newer German armour. As early as 1943, this was recognized, particularly in terms of armament, prompting the British to upgrade many of their Shermans with the 17 pounder AT gun. Army Ordinance refused to upgrade the gun for a variety of reasons, and it took both field experience and considerable pressure from commanders to get upgunned Shermans to the field. By late 1944 and early 1945, heavier versions of the Sherman would become much more common. However, even the 'definitive' version, the Easy8, was still under gunned and under armoured against the Panther and the Tiger series. The Pershing, the American heavy tank (which would eventually become the Patton) was not produced in significant number until very late in the war. This was a tank that could provide good protection and good penetration, but was not considered important enough until it was basically too late to use them. How many American tank crews died for that? And Army Ordinance's reason? Because they didn't want to disrupt production, and didn't feel that the expense was worthwhile. They learned their mistake.

Or, what about American bomber tactics? I suppose there's an argument to be made that daylight raids were more humane on the bombed civilian centres by theoretically limiting casualties, they also significantly increased the risk for bomber crew.

That said, the American forces were significantly better equipped in other areas, particularly small arms and support vehicles, than their German counter parts, and there certainly were a lot of armoured vehicles in the American cupboard. But I don't think there's any evidence that the American commanders were anything less than aggressive with their forces, and were willing to expend whatever manpower was needed to take their objectives. There are certainly instances where attacks were delayed or areas of strong resistance bypassed, but the idea that the American military of 1944/45 was any less willing to lose men than it's opponents in Germany is probably best described as an anachronistic application of modern American military doctrine backwards.