Yes but times have changed and I think, depending on where you live in the world perhaps, that there is a growing expectation that you should be allowed to delete your digital tracks.
There's a certain level of hubris to an attitude in which a given site that feels it's needs are more important than users.
Saying you can't delete all your posts/account is the same as saying "you do not have the right to control your own posts here".
I think it should be OK on HN to delete all your comments on your account if you want. I appreciate that this would degrade the quality of impacted historical comment threads but hey that's the price for giving people back control over their digital lives.
It happens on Reddit and whilst every now and then I encounter a reddit thread with deleted items, in general it has not destroyed reddit, and I respect the right of those users to have deleted their digital comments.
I rate respect for user wishes over the importance of maintaining historical threads integrity on HN.