Modern twist on 70's speaker design?

These still exist but mostly in the realms of the pro world. The wives of most consumers want lifestyle products not ugly boxes

Here are a few models to check out:
Tannoy
JBL
Westlake
ATC
PMC
Meyer

Many models come with 12" and larger woofers - some with dual 15". New they are not affordable(as they often use very expensive pro audio drivers). If, however, you consider second hand then some JBL 4435's can be had for around $3000.

Klipsch Heritage - LaSacala, Cornwall, Heresy and Klipschorn

If you'd like a $30,000 boutiqey product (straight from the era of excess) check out the Shindo Latour, built around good ole Altec horns and drivers and Altec 15 inch woofers.

check out Audiokinesis, grown in idaho. I've heard them and they DO rock. They don't meet your three way, 15" woofer criteria, but have 10" woofers and a horn tweeter

Jazz Modules are $4500 ... is that affordable?

http://www.audiokinesis.com/product/content_audiokinesis.htm

The 70's are still here, as Wpines has pointed out. Klipsch Heritage.

the only affordable speakers of that type still available that i know of are cerwin-vegas. i've always thought that everyone should have a pair hidden in the closet for the times when your friends have gone, and you want to raise the roof a little.

Here you go...

http://www.amazon.com/Cerwin-Vega-VE-15-3-Way-Speaker/dp/B000EI0EBS/ref=sr_1_2?ie=UTF8&s=electronics&qid=1241819125&sr=1-2

Both Absolute Sound and Soundstage did favorable reviews on the 51"
tall 115-lb. Cerwin-Vega CLS-215. It has two 15" woofers, a 6-
1/2" horn-loaded cone midrange, and a horn-loaded dome tweeter.
Claimed sensitivity is 97 dB, but Soundstage's tests measured it at a still-
high 91.5 dB. These things make bass effortlessly down into the mid-20s and
can soak up 450 watts without cracking up. Both Soundstage and TAS said
unequivocally that no other speaker begins to give you this level of scale and
dynamic range for about $1K/pair.

To answer your question, however, I think 15" and 12" woofers
made way for 8" and 6.5" woofers because the smaller diameters
make for faster and more articulate bass, and the smaller diameter allows for
a narrower front baffle for less front baffle diffraction and a smaller footprint.
Basically boxes gave way for less obtrusive columns.

Note, however, that it would take seven 8" woofers to equal the pistonic
area of the CV's two 15" woofers. Or nearly eleven 6.5" woofers.