Hasn't that silly version of the comment definition died yet? (: Everyone not obsessed with reading official standards knows that HTML comments simply start with <!-- and simply end with -->. I'm surprised you didn't demonstrate whitespace between the -- and the >.
In my experience, the facts of the HTML standard on this point usually lose to the much simpler common misconception of what an HTML comment is. And I'd be quite surprised to find a web page that used a comment that included --> in the middle.
If I found the real definition of the HTML comment technically preferrable (or if I didn't feel that the tide had already turned on this), I'd probably be fighting for standards conformance. As things stand, I tend to prefer de facto standards conformance on this point (though with a small spark of guilt).
Note that PerlMonks gets this and one other small point of HTML intentionally wrong to better deal with HTML produced by the wide variety of users typing it in "by hand".