If the thread is too old to take replies, I'm not sure why the OP isn't deleted.
I'm finding it hard to argue with you on this one, although I do understand why your post was deleted. Most of the time when someone necrobumps a thread that old, it's because they need to post for their sig campaign or bounty and somehow they've run out of threads in which they can write something. In your case, your intentions seem to have been genuine....and yet there's a rule against bumping old threads....and yet those threads remain open.
There is generally a higher threshold for a new post to be on-topic when the previous post was made a long time ago. In many cases, it would be better for someone to create a new thread instead of posting in an old thread. If a post is not substantial enough to account for making a new thread, it may not be appropriate to create the post. One reason for this is because once a thread is bumped, everyone is encouraged to read it by way of the thread appearing on watchlists, and at the top of the sub it is in, and is marked as having new replies. Someone reading to an old thread may reply to the second or third to last post (for example), that may have been written months or years ago, and now contain outdated information.
May I suggest that, when the reasons are "other" that some guidance be provided so that I may "avoid posting things that need to be deleted"? The quoted email reports on a reply which was definitely on-topic, and I have no idea why it was deleted.
I do agree that it would be nice for the mods to have an option to give a more specific reason as to why a post was removed. Currently, some mods will send an (automated) PM from their forum account for certain reasons, however not all mods do this, and this invites mods that do this to receive excessive number of PMs from forum users.