The norm of large-scale composition is for a motive to be established on the surface and then for there to be hidden repetition, whether the camouflage takes the form of ornamentation or augmentation.
George Gershwin’s music, however, has a number of notable reversals of this norm of motivic presentation, and his well-known reliance on improvisation as a compositional tool might be the most likely explanation. One can imagine an improviser “analyzing” on the fly, so to speak, and then bringing middleground features to the surface. On-the-fly analysis is not what Schenker meant by “aural flight,” but it is consistent with the idea.