This explanation makes sense, but I can't reproduce the behavior.
in IE ... all elements with IDs are already in the global scope
This I can confirm. If the page contains this:
<div id="bob">Hi</div>
bob == $("bob")
The issue comes when you do something more like this.
<script> var bob = "hello world"; </script> <div id="bob">Hi</div>
One might expect this, given the above, but I tried it in both IE6 and IE7 and the global keeps the value it had before.
var bob = $('bob'); is a useless statement in IE.
The issue comes when you do something more like this.
<script> var bob = "hello world"; </script> <div id="bob">Hi</div>
now bob doesn't equal "hello world". Your global has been clobbered.
---
Similarly, it's surprising how many people fall into this trap:
<input type=submit id=submit>
Well that's all great and everything, but you've just clobbered the submit() function on the form.
before:
form.submit = function()
now:
form.submit = Your dumb input element.