Most were, including the very popular A25 and less expensive models, but 'upscale' models like the A35 and A50 used two-chamber sealed cabinets with the damping created by a port between the two chambers to control the woofer at resonance and behave as a sealed enclosure below that, as explained on Greg Dunn's Dynaco page:http://home.indy.net/~gregdunn/dynaco/components/speakers/
Later on, David Hafler produced speakers with frequency-dependent loading under the Hafler brand, North Creek made aperiodic-tuned speakers, and Morrison audio omnis have a multi-chamber cabinet designed with the same goals: Tight driver control and flat electrical impedance.
I know of no inherent reason why an aperiodic design can't produce impactful bass unless one is addicted to high-Q bass at resonance. The A50, with two 10" woofers, could produce plenty of 'slam' when called for. I suspect that with modern CAD tools for driver and enclosure design and testing/measuring, this approach could yield even better results than the classic models of the past, even though the higher power amps of today aren't challenged as much by high impedance spikes as the amps of the Dynaco era (Dynaco's best-selling amp when the A25 came out was the 35WPC tube Stereo 70).
As far as the Scanspeak items depicted, I don't know how well they'd work with a one-size-fits-all approach. With the A25, Dynaco tuned each individual system by feeding a low frequency square wave into the speaker and watching the driver behavior on an oscilloscope while adjusting the vent resistance by adding/removing stuffing. (And worth mentioning that they did it for eighty 1968 dollars MSRP; my, how the business has changed....)