With "frequency response specs," do you mean curves (and +/- dB tolerances) or simply numbers indicating frequency extension up- and downwards?
If the latter in particular I'd say specs are pretty much worthless. Of course a stated steep roll-off below 80-90Hz would indicate to most, or so I gather, that sub-augmentation is needed, but hopefully a purchase is based on actual audition (and the added information that can be had by simply looking at the speakers and knowing their driver implementation) than dwelling on mere numbers. Certainly the actual bass quality (what's the spec-numner for that?) in its central region is wholly more significant.
Whether a speaker rolls off above 16-17kHz or 35kHz (or even 80kHz) and what this means in regards to audible significance at large I'd say is completely irrelevant; in fact I'd call it marketing BS to claim otherwise. If anything frequency irregularities (i.e.: peaks) above what is regarded the limits of human hearing may or may not impact on perceived sonics.
Where curves are supplied the challenge, as with spec numbers, is their measured context and overall trustworthiness, and in any case I don't see what can be deduced from them being remotely as informative as actual listening. It's indeed critical, and oddly interesting when so much emphasis is placed on frequency extremes, primarily from reading specs, when what's audibly between is so much more interesting.
