I'm fairly sure that the "4.2.2.x was never meant to be public" line is a myth. Though the NANOG thread cited in that post is good historical background, it is contradicted by more modern sources:

"[...] DNS infrastructure is largely split into two types; open (public) and closed (private). Open DNS is provided by companies like OpenDNS, Google and Level 3. You can use it wherever you are on the Internet with no restrictions or authentication required."

- Mark Taylor, VP at Level3

http://blog.level3.com/level-3-network/a-flawed-study-of-cdn...

I can't find any cite where anyone else who I would consider a reliable source in the DNS world (Vixie, &c) repeat this claim. To the contrary, Level 3 is often grouped with Google, OpenDNS and others in discussions of open public resolvers [1][2][3], and those in the know never seem to speak up and say otherwise in these discussions.

That being said, I have absolutely no personal knowledge on any of this.

[1] http://www.maawg.org/system/files/Fergie_DNS_Open_Resolver_M...

[2] http://markmail.org/message/gh7f2wvfbn5mpvuq

[3] http://www.circleid.com/posts/87143_dns_not_a_guessing_game/...