OK, this is possibly a controversial suggestion, and I'm not entirely convinced by it myself, but I figure I'll put it out there to see what people think.
If we take the standard description for what comments are for, in this case taken from the Stackoverflow privilege page:
Comments are temporary "Post-It" notes left on a question or answer. You should not expect them to be around forever: Once a clarification has been made, an edit added to the post to include new information, or the issue in the comment is otherwise resolved, it is subject to deletion. In reality, many obsolete or chatty comments remain untouched due to the high volume of comments posted, but this does not mean that they can't or shouldn't be deleted in the future.
When should I comment?
You should submit a comment if you want to:
Request clarification from the author;
Leave constructive criticism that guides the author in improving the post;
Add relevant but minor or transient information to a post (e.g. a link to a related question, or an alert to the author that the question has been updated).
None of these reasons really necessitate a comment existing forever. Requesting clarification and leaving constructive criticism are useful to get the OP to improve their post. Which they may or may not do. And the ability to add relevant, but minor info such as links to other posts can be handled by the 'related questions' in the sidebar.
People spend a lot of time concerned with comments.
I could go on.
So is there really a reason they should stick around?
I propose this idea for discussion:
A comment will only be visible for 48 hours. After that point it will be deleted from view. That should be enough time for the OP to see it and act upon the suggestions in the comment. Any comedy comments would have been seen and everyone would have enjoyed them at a the time, but 48 hours is a long time in the digital world, and questions that old are basically consigned to the files where they're of most benefit to people searching via site search and Google, and these people don't really care about the comments - they're there to find the answer to the question they were searching for. (And if you think that, just because there are comments there that means people will actually read them then you're mistaken. Nobody actually spends time reading things on the internet these days)
I'm sure some people may say that there are sometimes useful links, comments, info posted in comments. So perhaps as a compromise we can keep comments persistent that recieved >5 votes. I don't know. But basically, binning off all the comments after 2 days would clean up the sites and potentially stop people being so precious about them and reinforce the idea that they are 'temporary Post-It notes'.