Low-sensitivity speakers — What's special about them?

What it comes down to is... really good mids with any type of top end extension without cone break up is hard to find in true high sensitivity speakers.  It has already been mentioned about bass.... The bigger the magnet/motor structure of a woofer, the more sensitivity and the more mass it needs to produce low fs/Qts.... these are attributes that lead to deep bass.  As you as you ad mass fs goes down and qts goes up,  but the trade off is that sensitivity goes down.  
Its not a perfect world.  I try to find the sum of parts as a whole to start the design process. Not being able to find any single part can kill an entire speaker project.  
Alot of people really like sealed box speakers for bass, I am one of them, but woofers that work well in a sealed box need a qts of a minimum of .4 and preferably .5 or even a bit higher.... Look at spec's on high sensitivity woofers,  you'll see .2 to .35.  This is just too low to produce bass in a sealed box system,  Although .35 can produce very satisfying bass in a ported or vented design.  You also have to consider that most good designers prefer to keep the crossover out of the vocal range,  so again,  it requires drivers with a fair amount of extension on the top end or bottom to pair with other drivers. 
There are plenty of excellent parts to design high quality low to medium sensitivity 2 or 3 way systems with great results. 

@phusis 
So you say "Percieved" and that these mid and bass drivers with good extension and little cone break up are readily available.... recently I've shopped a few hundred drivers looking for such.  Please list the model numbers.  

@phusis
My original post towards this subject was dealing with what it takes to design a true high sensitivity design that is capable of audiophile use. That is why I posted a few driver spec's in that post to make sure knowledgeable people knew that I was referring to drivers. 
Yes, in general,  I was speaking of cone speakers and woofers in general.  Many may not realize that MOST cone mid range drivers are woofers that have very good top and bottom extension.  The higher in sensitivity that you shoot for,  In general, the worst the top and bottom end extension gets. 

Hi @phusis

Not sure what we’re doing here, but I’ll bite. I assume that you are simply saying that it can be achieved with horns. The Lamar driver is very good for sure. Its top end extension lacks, but its nice sounding, fairly linear (plus or minus 5db from 200 to 2500) and can cross as low as 80 hz. Yes, add a tweeter and you’re good to go. So, thank you for posting 1 horn driver that is capable The 12a horn is huge and you are correct, this has not been the target in my designs.Something a little more compact. I’ve been looking for a couple of parts... a 12 to 15 inch that is closer to plus or minus 2 from 40 to 1500. I’ve contacted 3 manufacturers, I’m told that it can be built for me, but as of now is not out there. The AudioTechnology Flex 15 is close but its only 93db. and its only getting 93db because of its very low QTS of .22. Another factor is trying to get a woofer.  I'd really like to have more like 97db and I need some xmax. Most every driver that comes close to what I’m try to achieve has a very low xmax. Again, I’m told that I can have it manufactured, we’ll see.

I have very specific design parameters that I'd like to achieve.