Why are .innerHTML problems not an issue when using JQuery().html()?

Question

I worked out any single instance of document.getElementById("MyID").innerHTML = "A value" in this Javascript World Clock guide causes Wordpress Admin not to load completely and breaks various areas of the Wordpress admin interface.

I solved it by replacing each instance with jQuery("#MyID").html("A value")) which appears to work fine. What is causing .innerHTML to fail miserably but not JQuery().html()?

Answer 1

At a guess I would suspect either browser-specific stuff or document.getElementById("MyID") returns null, causing an exception.