That's not true in many cases. As soon as you put shims to level the stand it bears only on those points.
.........which is why you shim as much of the perimeter as possible. I would never shim it at only one or two points, I would try to shim any part of the stand that does not contact the floor. My floors are level, and I have w/w carpet and pads, so low spots and such have never been an issue for me. Where possible, I believe it is preferable to shim the tank rather than the entire stand.
My point is, if you are going to have four legs that are the only transfer points to the floor, then you probably need bigger stock than if you are skirting the whole perimeter of the tank. I've looked at a lot of cabinet-style commercial stands for 75g, 90g, 125g, 180g tanks, and have never seen them use any 2" lumber.