Nope. Sales is NOT a liability, and there is no accounting fiction. Sales are also not an asset. They are an income. The money earned from the sale is the asset. I think you may be confusing ledger credits with liabilities.
All credits are not increases in liabilities, but all increases in liabilities are credits.
Good background on Wikipedia: [ http://en.wikipedia.org/wiki/Debits_and_credits ] [ http://en.wikipedia.org/wiki/Double-entry_accounting_system ] [ http://en.wikipedia.org/wiki/Accounting_equation ]
And I see capital is shown in the balance sheet in the original post as well - but what struck me as counterintuitive in the original post is representing sales as, effectively, a cash flow towards the customers. If not a fiction, surely you have to grant it's an abstraction.
See this tutorial as well: http://www.principlesofaccounting.com/chapter%201.htm