Is it that New Atheism isn't philosophy?
Yes -- it is not a philosophy; wikipedia describes it as "a social and political movement" first associated with Sam Harris, an American writer who holds a B.A. in philosophy and a Ph.D in neuroscience but does not practice either professionally in the sense of having academic tenure. Harris's works appear to be bestseller non-fiction, a category which includes celebrity biography, self-help, travelogue, etc.; Harris is a popular writer and "New Atheism" is a essentially a populist movement.
I have participated in online atheist discussion groups with people who would be considered part of the "New Atheist" movement, and they are, like most religious practitioners, not particularly interested in philosophy. By this I mean, most of them (like most churchgoers) have never read a single volume from the Western canon (almost however you want to define it) and most likely never will.
I think the significance of "social movement" may need a bit of explaining for people who live outside of (particularly the southern) United States. In most of the western world it is probably not a big deal to be an atheist; there is no great social tension around it. I currently live in Canada and a decent proportion of average, non-philosophical people will casually admit atheism; if not, they are not particularly upset by it.
However, this is not the case in most of the United States. Even when living in liberal, multi-cultural New York City -- a generally fantastic place -- it was very rare for me to meet someone who did not claim to believe in God and profess one religion or another. Further, while I was never made to feel uncomfortable as an atheist, it was a bit bizarre to sometimes be an object of curiosity ("I've never met an atheist before...", "What does the atheist have to say about this?", etc), as opposed to here where the topic is generally considered too dull to bother with.
In other parts of the U.S. the situation is considerably less palatable for people who publicly deny the existence of God. For example, in many U.S. states, atheists cannot legally hold a public office.1 This is not a context in which a philosophical movement is very useful. An average person in the online discussion groups may be a young adult living somewhere where he/she does not know any other atheists and may already have been subject to repercussions amongst his/her family, at school or work, etc. To these people, the discussion groups offer encouragement and hope in the form of a positive, progressive social movement. Some of them are interested in reading (or may have been motivated by) Dawkins et. al., but most of them are not. They enjoy commiserating with other people about their predicament, and many of them do end up finding people to connect with in the real world because of online acquaintances.
The average atheist, like the average theist, does not consider his/her belief something that needs any particular tuning and so the idea of doing copious reading to support it is besides the point.
This is why such groups often bar argument about the topic. I.e., if you join up and then say, "I'm a theist here for a philosophical debate!", you will politely be told that is not welcome. They are not there to argue about it any more than the person who shows up to church on Sunday.
1. Note that these laws have long been deemed invalid by U.S. Federal Courts, however, they still mysteriously exist, with occasional minor consequences. Further discussion and references are in the comments. Please also note I am not trying to argue for the "New Atheism" movement but only explain some of its self-justifications, which (for better or worse) often include citing these State laws.
