Proceeding from simple resonance structure arguments, it is proposed that the softening of the resonantly enhanced Raman modes with conjugation length in extended pi-systems reflects primarily the nature of the ground-state adiabatic potential energy surface for the corresponding polymer. Therefore nondegenerate conjugated polymers and their oligomers differ principally from polyacetylene and polyenes which already approach the degenerate state for finite length. Model calculations employing the LHS Hamiltonian confirm this notion and reproduce correctly the experimentally observed trends for polyacetylene, poly(p-phenylene), poly(p-phenylenevinylene), and their oligomers.