Checking with some people here, it's actually more complicated than this: what I described is true for IE9 and below, but for Firefox, Chrome, and IE10 measured page load time will include execution of these deferred scripts.
I was going to include Google Analytics site speed data, but it seemed less accurate than NewRelic's Real User Monitoring.
(Disclosure: I used to work for New Relic)
[1] https://developers.google.com/analytics/devguides/collection...