Federal gun laws are the epitome of this precept in action. Depending on when a gun was made, the exact same firearm can be legal or illegal to possess. A folding stock on a pre-ban semiautomatic SKS is legal, but illegal on the post ban weapon. Not to mention that functionally, there is no difference between a pre and post ban weapon for the most part. The purpose of the law is only to create traps. Keeping track of these regs is all but impossible for most people.
So when you say that the law doesn't do anything, you are very mistaken. It can be used to write regulations which act as regulatory traps to ensnare innocent gun owners. If you don't think this power cannot be abused, you have been awake with your eyes wide shut. Just think of what would happen if some future president issued an executive order to enforce all firearms regulations and punishments for violations to the letter and to the max...after offering say, an unconditional amnesty for anyone turning in even possibly illegal weapons. Many people would turn in their guns just to be on the safe side.
As for Bush, he would and will sign this in a heartbeat, and for those who think the House will sunset it automatically, don't. Bush would and I predict will pressure House Republicans on the fence in safe districts to support this legislation and get it over the top in exchange for something else he wants. Bet on it.