That's perfect if you're trying to save money, but things aren't always about saving money.
For me, having an iPhone for an extra 3 months was worth the $1000 (my old piece of crap barely made phone calls and weighed more than my luggage), so I don't regret buying it 2 days after it was released.
But your rule is especially good for saving money on computer products, eg hard drives... it always seems to be the second biggest hard drive which is the best value.