it's not obsurd at all. the only way a program can distinguish files (excluding hashes, because that's what we're calculating here) is by the full pathname of the file. otherwise, something like:

/vacations/jamaica/flower.jpg
and
/vacations/hawaii/flower.jpg

would could be considered the same if the sizes were the same.

when LimeWire starts up it checks to see if the files you're sharing match any recorded pathname, and gets the existing hash. if it doesn't match, it recalculates the hash and stores it, purging info that no longer exists in the filesystem.

i really don't see what the large problem is. when you move files, it'll rehash the first time it encounters the new path.