Yes, lots of other places are peppered with 'comment deleted because...', but a moments thought would surely reveal that those other places are not in the same league/class as this Forum, or any other Community Centred round-table news'n'views format.
-The minute the allowable content here became codified much of the Forum's posts would contain argy-bargy over whether the 'laws' are being correctly applied. Howard, for it is he in the main, would go from being 'the voice of reason/school-bus conductor' to 'judge-jury-executioner' all rolled into one. On the whole the current overriding expectation that we are all adults and should know where the line is drawn works 999.9 times in every thousand.
-Self-deletion can occur for many, many, many reasons, and if each time the same notification is shown in it's stead we all would be none the wiser as to quite why the deletion has occurred.
Yes, I agree that on the very rare occasions when a post is self-deleted, and when it has been commented upon, those comment tend to 'dangle' and their sense is lost - such is life. Consider the occasions when a member storms-off in the huff (high dudgeon, is a lovely phrase, but that is by-the-by) and 'demands' that all their comments and photographs be removed...what then?
This issue hit-home to me once recently. When somebody posted a link to their own spoof video, cruelly mocking something local that (as far as I am able to tell) richly deserved mocking. That member had second thoughts, and the rest of that particular thread was about what the deleted link could possibly have been. The matter was resolved by somebody posting another link to the 'highly amusing' video, but for a little while I was ever so slightly irked - and yet I have no grounds for asserting that 'I' should not be made to feel that way - such is life.
Finally,
This being more 'club' than truncheon it is always possible to enquire of either commenter;they who post & delete and they who address the now deleted post, as to what happened. Let us not get all uppity and demand or expect that what happens here differs materially from face to face encounters, bits of all conversations between others can be lost to a third party, not much of which was ever worth knowing. Things can stay as they are or get much worse. Thank you.

Ignorance is bliss, bliss is happiness, I am happy...to draw your attention to the possible connectivity in the foregoing.