Files are forever stored in the network and this is a costly feature for the network in the long term. It would be unfortunate to not use this feature by generating URL that aren’t forever valid.
First, a concrete application is the end of favorites list with links that have become invalid in them.
Then, there is the transparency of the network. I have argued a lot in the name of transparency to reimplement SD deletion to prevent recreation of a SD with same key, same value but a different content. It was hard to convince Maidsafe but finally it was accepted. Here I feel the same and I think that sending a link that you can invalidate later is not transparent.
Imagine that Maidsafe implements both kind of links to satisfy both of us. Which one do you think users will prefer? Permanent one or removable one?
Maybe some companies and governments could prefer removable ones because they want to be able to remove some information that have become compromising to them. But I am sure that consumers and citizen would prefer permanent ones, simply because this is one of the founding features of the network.
This is the reason I like file URLs implemented as base64 encoded datamaps. Like hashes in the bitcoin blockchain they cannot be compromised. They are bigger but they are still manageable and above all, they give access to the files, contrary to the hashes in the blockchain.
Another argument, but a technical one for @ben,
I suppose that @happybeing wants links that can be invalidated by a deliberate action of the sender and certainly not as a side effect of another unrelated command. I am not sure of the object whose address you think can be used as the URL, but I am afraid that a simple action as deleting or adding another file in the same directory can invalidate the URL.