125's are pretty good at weight distribution because most are 22" tall but only 18" wide.. so the weight is not that concentrated.
for larger tanks, it can be a problem.
take for example my 150g (72x18x29). you have 7" of extra water column (about 330 pounds of water) + the tank itself weighs 100+ pounds more than a standard 125.
so you have almost 450 pounds more weight the exact same area as a standard 125.
hence the reason why tanks over 125 need special consideration.
the 180 size is not as tall, but you have again, 30g more water + a heavier tank which is a lot of extra weight
the 220 size, well, that had better be on concrete or ground level if you ask me