The concept of ''natural'' longs and shorts applies to futures mkts, not equity mkts. The reason this is the case is that these two broad markets exist for different reasons.
Equity markets exist to facilitate capital investment and provide for transference of ownership; futures mkts are mechanisms for the transference of risk. Both have speculative components in their makeup, but speculation is the raison d'etre for neither one.
No one, bar the proprietor of a business, can really be said to be a ''natural'' owner of shares in a business. Equally, no one -- as you point out -- is a ''natural'' short for shares. The other way to say this is to define a ''natural'' as a person or institution who, because of the nature of their business enterprise, will almost invariably be participate on just one side of a (risk transference) mkt.
Does this clear things up a bit (hope, hope...g!)?
''...because of the nature of his/its business enterprise, will almost invariably participate on just one side ...''
Posted it too quickly, my apologies.
Yeah, I kinda suspected that futures might be inherently different from equities in that regard. Thanks!