Jim> It's not just that either. With the stock sprocket, it's quite a job to change them out: the wheel has to come out, and there's some dismantling to be done. Some here may say otherwise, it depends on how much of a mechanic you are, but the "carrier" type sprockets go on so easily (no need to take the wheel out) that for me, it made the difference between having the sprockets changed professionally, at further cost and inconvenience, and doing the job yourself.
All that said, if you do few miles and/or don't intend to keep your bike for years, it may be hard to justify the initial cost.