Thiel Owners

The 3.7 does not lack bass. It is very difficult to achieve the bottom octave with medium sized cabinet designs, especially when using 1st order crossover networks. (Woofer must be expected to perform equally well several octaves above the crossover point.) Typically designers have used much larger cabinets or electronic equalization, but that becomes taxing on the amplifier. I was impressed with the bass output of the 2.7 and I'm sure if you audition the 3.7 you will not be disappointed in the bass output.
I must add also that I agree with unsound as far as room size. Treatment for room interactions can make a huge difference in the mid and upper octaves. Bass, deep bass, would then be the limiting factor due to wavelength and the 3.7 doesn't quite get there.

 jetter, I can only hazard guesses as to what Jim Thiel had in mind.
 But, first of all let's clear up the idea that the 3.7's lack bass, they have good clean bass until all but the deepest 1st octave. Perhaps, Jim Thiel thought that since most music (about 80%) is in the midrange, that there is limited musical content in that first octave, that many don't have the rooms to accommodate true full range bass, and if they did have the room, that deep bass might be better managed by his dedicated sub woofers. 
  The only question I would have for him is why he didn't use the superior time and phase attributes of a sealed box design in the 3.7's, especially if he was willing to sacrifice actual deep bass response? Sealed boxes might have made the transition to his sealed boxed sub woofers smoother as well. 
 A speaker capable of full range bass response would probably need to be considerably larger, and more expensive. As such perhaps more people and a correspondingly larger market share would see greater value and WAF in the 3 series with somewhat(!) limited bass response. Those  who wanted deeper bass response could augment the 3.7's when space and funds availed themselves.
 Jim Thiel has hinted that the 3 series had for some time become the sweet spot as the value to performance leader in the Thiel line up. I don't think it would be unfair to suggest that the original CS 3's were the ones that really put Thiel on the map.  I can only speculate that if Jim Thiel wasn't so abruptly taken, that he would have went on to develop more, even higher end projects that went beyond the 3 series. 

Thanks Robin and unsound, for clearing up that it is only the deepest octaves that are lacking.  In that regard I unconditionally like subwoofers anyway and will always have a couple.

I have shied away from Thiels in the past because there was always their reputation (deserved or not) that they were hot on top and because of the massive clean power needed to drive them.  But now that Jim is not around it seems that their is a renewed interest in the speaker, a reverence being paid t the genius.

I have never seen the 3.7 in person, but it looks great in my opinion, if not a bit stunning.  And I am thinking of trying it with a mega watt ice or ncore amp and tube pre. 

^A lot of Class D amps might find the Thiel's impedance challenging.
Jim Thiel thought Class D amps were best left to sub woofer use, of course a lot of Class D development has happened since then.