The "vs." in the title is deliberate. My explanation of that is the theme of this post.
Gnu Atheists, more than many Old Atheists, in my opinion, focus their attention and attack on, and scorn for, all shades of Christianity and other religions, on doctrinal belief and practice issues. They ignore other elements of religious belief in general that any thumbnail-sized introduction to philosophy of religion or psychology of religion would teach them about.
This may be somewhat of a dividing line between Old and Gnu atheism, or maybe not.
But, Gnu Atheists, while not, in general, politically libertarian, are often socio-culturally libertarian, or anti-communitarian in some ways. (Except when it comes to conventions, perhaps.) There's nothing wrong with that. But, to not see that as a backbone of many people's religious belief, or non-religious humanism, even , is a big blind spot. A HUGE blind spot.
An unemployed southern Baptist isn't so much looking for a miracle job from Jesus as he or she is a job-hunting support group at the local Baptist church.
Now, since atheists of any stripe, or even atheists plus agnostics, are about as uncommon in American society as Macs in a PC world, it's harder for atheists to create this type of organization.
who are actually growing indeed (self-identified atheist and agnostic numbers are NOT) they'd be well served with taking a page out of the secular humanist playbook, whether via Ethical Culture, select Unitarian churches, or some other vehicle, and finding out how to be more sociable and more sociological-minded.
That said, I don't really see that happening.
Now, is this to say that theology and dogma don't matter to believers, even when sociological and psychological concerns weigh heavy? No, of course not.
If nothing else, belief systems, matters of belief, doctrines, creeds and confessions have major sociological utility for dividing the in-group from the out-group.
An aside: The fact that just 1.6 percent of Americans self-identify on the ARIS survey linked above as atheist or agnostic, while 12 percent, in response to a different question, show an atheist or agnostic "metaphysical stance," says several things.
1. Contra ARIS researchers, many people do still see a stigma in calling themselves agnostic or atheist.
2. Many people still don't know what the two words mean. (I can attest to that.)
3. The growth of Buddhism, where Theravada practitioners, for sure, and many others, are metaphysically atheist but still quite religious, is a confounding factor.
For more on the first two points, see this essay on ARIS research.