Why not acoustic suspension?

Yes the air in a closed box affects the driver suspension. But it's only acoustic suspension if the air is more significant than the spider. When Edgar Vilchur designed his prototype he used a regular driver but cut away most of the spider so it no longer controlled the driver motion. Putting it in a small box allowed the air to bring back control. The claim was the air was more linear than the spider.

Closed box roll off is always ultimately 12 dB/octave. What varies is where roll off begins and the shape of the bass curve before hitting 12 dB. Poor design can cause a hump before roll off(any Q above 0,707). A good example is the BBC LS3/5a with a Q of 1.2. But the BBC did it to make it sound bassier than it would with a tight Q where the speaker would have sounded thin because the box resonance was so high. They sacrificed definition for bass balance.

I just learned something new.  I guess there’s a range of suspension / box configurations.  To me it’s all AS, but I guess in the formal sense, a true AS has to have a soft, compliant suspension.  

Modern speakers often have stiffer suspensions and while the air in the box is important in terms of the suspension it’s not as dominant. 

I stand corrected, my thanks and apologies.  I learned something new! 

Among the many differences of the modern sealed approach apparently is the reduced sensitivity to the box size.   This used to be a big deal.  

It's not UNIMPORTANT, but with the dominance of the driver suspension it can't hold as much sway as before.  

So are there many acoustic suspension subwoofers?

The AR 1W must have been the granddaddy of them all.

I guess the Sunfire True Sub was not technically acoustic suspension because it used a passive radiator?

@61falcon 

"Can anyone name modern acoustic suspension, true acoustic suspension speakers made today?"

The ATC SCM7 - SCM20 series are acoustic suspension which refers to any speaker whose woofer is mounted in a sealed encloser where the air trapped inside acts like a spring stabilizes the loose and floppy cone suspension. Acoustic suspension is also known as an infinite baffle.

The advantages lower frequency extension, a more benign or smoother impedance modulus and lower bass distortion. The disadvantages are mostly dramatically less efficiency requiring a more powerful amplifier. 

It was common to see rather large enclosures at one time with woofers of twelve to fifteen inches or more that could reproduce bass notes as low as 15Hz. Some of these were produced by ADS, Avid, Cerwin Vega and others. The Advent Loudspeaker, the Acoustic Research AR 3a though smaller than the above were still fairly large with up to two square feet of internal encloser volume. Radio Shack also marketed quite a few fairly large acoustic suspension speaker systems.

BTW, I asked fellow hobbyists at DIYaudio, and the consensus is that we still call a box with a driver in a sealed box of small size "acoustic suspension." 

The drivers have changed over time but a sealed box is almost always acoustic suspension.  Disagreements should come over to DIYaudio. :)