I agree with you.
Existing customers get cash-back for every purchase. There are numerous give-aways for all. There are often coupon codes for existing customers.
What is making people unhappy is the 25% off, which is a big savings, but from where I'm sitting, I don't really think that SSC is in any way obligated to include everyone in such an offering. As you have very well put it, this is a business strategy. You can't blame a company like Sideshow for doing this. Recruiting more customers.
The example with the credit card companies is very good. You see these kinds of lower introductory rates all the time. Same goes for many, many other businesses.
People feel almost insulted by this. I really think people need to chill out. Walk into their collection room and feel happy about themselves. You've got something right here, and right now, that all these new customers do not. They have a long way to go (and a lot of money to spend) before they are there. Take a moment and just relax, and stop taking things so darn personal.