There is a difference though. A small amount of inflation is considered good because it drives spending in a "use it or lose it" fashion. We have a consumer based economy so we need people to spend to drive things.
Any deflation is always bad. If you knew that your money would grow in value just by keeping it under your mattress, you would defer buying anything but the barest necessities as long as possible. Spending levels would drop and the economy would go into recession (or depression).