This is in accordance with Generally Accepted Accounting Principles, SFAS No. 109, "Accounting for Income Taxes".
The theory is that even if you don't owe tax today on a given temporary difference, you will one day owe (or get the tax benefit) of said temporary difference.
Remember: current tax expense= your tax bill this year
deferred tax expense/ benefit=your future tax expense or benefit on the book/tax temporary items