Here's a data point or two.

I built a large electric model with a group of guys for last year's DBF competition. Anyway, the basic plane was 72" span with a wing area of about 840 square inches. It had to be very strong, etc, so empty (but ready to fly) it weighed 11 pounds. That gives a wing loading of around 30oz/sq ft. Fully loaded with the two payload items it had to carry, it weighed 17 pounds, which brought the wing loading to over 40oz/sq ft. On a 30" span model, these wingloadings would have resulted in very bad manners. This plane, however, flew almost like a trainer. Even when fully loaded it was still easy to take off, fly and land. Only the landing rollout became much longer. (need brakes? )

Big models can handle much larger wing loadings, as the others here have already explained. Having enough power always helps also.

-David