It’s just data
If they're commented out then they can hardly be considered part of the page's metadata -- I mean, it's like saying that if the page contains:
<!-- <title> Foo </title> -->
...the title of the page is Foo. It's not.
I would be interested to see which (pingback or trackback) is harder to implement. Having implemented both, I'd have to say that Pingback was easier for me, but I think the real reason for that is mainly that the spec is clearer -- I kept running into edge cases that the trackback spec didn't define. On the technical side I found Trackback only slightly more complicated than Pingback.