The decision to make $ and £ different ASCII and ISO characters, and hence different keys, was deliberate, so that telegraphic messages didn't automagically read $100 on one side of the atlantic, and £100 on the other. Any currency messages comming accross with £ show up as #, not $.
Also deliberate was the recognition that people could use different characters to represent the $ and £ placeholder, if they weren't using $ or £. So the Americans simply replace the unused pound (LSD) symbol with the local pound (Hash) symbol.
Which is why my TV subtitles routinely indicate singing by bracketing it with £ symbols ...