Over in the HBO forum, RunningRiot voiced the common-enough question: why in-game and out-of-game pings to Halo servers often don't match up. Botman from Gearbox stopped in to provide the answer:

Let's say you can ICMP ping a host and average 80 ms. If the host's frame rate is 60 FPS, then your game ping time would be around 97ms. Now let's say the host's frame rate is 30 FPS instead of 60 FPS. 30 frames per second (1/30th of a second) is 33.333 milliseconds. So now your game ping time has gone to 113 milliseconds (80ms + 33ms). The game ping time depends on how quickly the server can respond to a client's request. The higher the frame rate for the server, the more rapidly the server can respond to clients and the lower the game ping time will be.

There's more detail to it than that, though, as well as a link to a longer article by Yahn Bernier from Valve on latency in games at Blue's News. Thanks Louis Wu at HBO.