Note: I eventually figured out that there was a firewall setting causing the issues, and have since switched back to the Google CDN of jQuery.
In testing JetPack, I noticed that jQuery wasn’t loading on my iPad or iPod Touch when connected to the corporate network. On 3G, it worked fine. I thought it might have something to do with the network’s firewall, so I tested at home, too.
jQuery worked fine on my iPad, but not on the iPod, which is about 4 years old at this point. Peculiar.
I loaded the page in Chrome on iOS and discovered that the Google version was, ironically, causing a browser security error. I switched to the version hosted directly at jQuery.com and the issue went away.