Right. If both dimensions of the cross section are 5-inches or greater, then the classification of "beam and stringer" and "post and timbers" applies. You can use a "beam and stringer" in compression or tension if you want. Likewise you can use a "post and timber" in bending. The point is that the grader looks at the pieces differently (with respect to defect type, size, and location) and the individual pieces have different design values. A 4x8 falls under the "dimension lumber" classification -- yet another set of design values.