LimeWire already matches files together if they're the same. LimeWire's definition of 'same', though, is 'exactly the same'. Replies transmit information that's not displayed to the user about the hash of the file -- that hash is used to group flies together. It's often possible that a file can have the same name & size, but a different hash. LimeWire won't group those together, because it'll cause corruption during the download.