bohman,

Are you referring to the aprons of the table/desk being perpendicular to the grain of the top?  If so, then of course, you would not want to tightly bind the apron across the grain of the top regardless of the type of wood (except plywood or other composite).  A 20 inch wide board has the potential for a fair amount of dimensional change through the years seasons.  The top should be fastened to the base with a system that allows the top to expand and contract.  One example would be to use slotted screw holes in cleats.  There are other methods as well.  There was a FWW article within the last year or two devoted to just this topic.

Still hoping that I have even interpreted your question properly; don’t fall into an assumption that hardwoods exhibit less shrinkage than softwoods.  Many hardwoods will change dimension a fair amount with changing moisture level.