Gaming mice tend to be held to a higher standard in ergonomics and comfort. If you use a mouse regularly, you will benefit from the reduced fatigue and chance of injury.
Higher DPI mice don't really give you a benefit of moving faster, as you can adjust sensitivity in windows and applications. They ARE, however, more precise at high sensitivity or high acceleration.
Think, for example, if you had an 800 DPI mouse on a 50" screen with awesome resolution. You would turn up sensitivity to a point that the software would be interpreting 1 dot as maybe 3 pixels to go faster. The result would be a noticeably less smooth feeling to the cursor or aim, especially when you moved quickly. You'd feel like you were using an old ball mouse.
In addition, gaming mice have features you'll never find on a 1000 DPI mouse, like weight cartridges, teflon (or similar) feet, on-the-fly DPI adjustment, extra buttons, programmable macros, button customization (either universally or per application), and on-board memory with custom profiles.
You can get a nice entry-level gaming mouse like the MX518 for about $40 (reference below), and I doubt you'll regret it. Is there a difference? Absolutely. If you don't care about precision or extra features, though, don't waste your money.