General Support: Re: Images in My Uploads
You've correctly identified that you can't delete or rename these attachments. Once they're attached then That's pretty much That.
They work in quite a different way to Assets - and this is largely because they're unique to each user (whereas assets are shared for an entire site). These are your personal attachments, which only you can attach!
One problem that would occur with deleting them is that anywhere that used the attachment (forum posts etc) would then be left with a link pointing to dead space.
Renaming them wouldn't cause that problem (since the URL uses the id rather than the name), but it was seen as a lower priority since the name shows up only to you, and not to any other users.
Furthermore, having different revisions of attachments does't make so much sense either. The intention really is that you just add another attachment, so that any of your old links point to the old version of the file, and new links point to the new one. (with Assets, you can add a new version without changing the URL, and revert to an earlier version if you wish)
Hope this helps clarify things!