There is not difference between
a) holding bitcoins and not use them.
b) holding bitcoins on SC and use them on SC (eg. trade on exchange if this SC is exchange)
They both have same value 1 BTC.
Sure and calculated physics in a vacuum is useful in space.
Theory and practice are different.
Even some bitcoin have different price than other bitcoin, or hadn't you noticed?
Bitcoin is not perfectly fungible with other bitcoin, why should you expect it to be so with SC-bitcoins?
(Want to buy some gox-coins?)