Your attitude is out of place.
Whether you choose to purchase the STS system is exactly that, your choice. No-one is forcing you to buy it.
Secondly, whether or not you invest in the STS, you need platemates or a system of small weight increments anyway.
If you are serious about your weight training and continuing to make progress with increasingly heavier weights, you need some system that will help you make those increases. How else do you plan to effectively and safely transition from, say, 20 pound bicep curls to 25 pound bicep curls?
You seem to be insinuating that SNM is personally responsible for the fact that the manufacturers of dumbells don't make them in 16, 17, 18, 19, 21, 22, 23, 24, etc, weight amounts.
Whether you use STS, any other of Cathe's weight training DVDs or do freestyle weight training on your own, you need platemates, or a system like them. I have them and they are a marvellous investment, better than all the other fitness gadgets out there. Again, your choice.
Clare