There is no free lunch. Moving to quad channel incurs more costs in pins, mobo traces, etc.. It's targeted product development.
Less sarcastically, what do people need >64 gigs for on a consumer desktop? I'm a dev and work on a pretty memory intensive service and don't need 128 gigs. Holding an entire double layer blu-ray in memory would only require 50 gigs.
VMs are my biggest memory hog, particularly when they are running lots and lots of separate Java processes.
It's usually foolish to say that we don't have need for more X in computing because nothing today warrants more than X; the thing is, if we have more of X, we find uses for it. Most of what we do can trade space for time, or incorporate things in cache hierarchies; and sometimes quantitative change adds up to a qualitative change because new architectural approaches become possible.
If I could have 1TB in my laptop, it would change the way we at my company develop software. In fact we'd rewrite our product to take advantage of that much memory, the case would be overwhelming; we'd introduce a new tier in our architecture for keeping a copy of the customer's working set (typically several GB) in memory. As it is, we rely on the database and its caching; it's OK, but it can't support all the operators we'd like to support.
I use mine as a terminal server to some super cheap Raspberry PI machines that are basically just monitors running VNC software.
For good performance you need about 4 to 8GB per user. I don't have that many users personally to need 64GB, but if you have a bunch of kids having terminals is much cheaper than a real computer for each user, plus you only need to keep one computer updated.
You could easily afford a computer in each room that way.