4.2.2.2 not responding to DNS queries

By default, my droplet (Ubuntu 13.04 x64) was set up with two DNS servers in resolv.conf: 8.8.8.8 and 4.2.2.2. In debugging why my client requests to Twilio were slow or failing, I found out that host resolution was timing out half the time and eventually discovered that 4.2.2.2 is not responding to queries from my droplet:

dierks@sharkodile:~$ host api.twilio.com 4.2.2.2
;; connection timed out; no servers could be reached

It works from my desktop in my office:

~ $ host api.twilio.com 4.2.2.2
Using domain server:
Name: 4.2.2.2
Address: 4.2.2.2#53
Aliases: 
api.twilio.com is an alias for public-vip374d1ca4e.prod.twilio.com.
public-vip374d1ca4e.prod.twilio.com is an alias for ec2-174-129-254-101.compute-1.amazonaws.com.
ec2-174-129-254-101.compute-1.amazonaws.com has address 174.129.254.101

This could be specific to my droplet or to DO. It’s not a big concern for me (I just replaced 4.2.2.2 with 8.8.4.4 in my config; Level3 apparently doesn’t want the public using 4.2.2.2 in the first place), but I thought I’d see if anyone else was seeing this problem and possibly contribute if anyone else is trying to debug similar problems.