You are making a valid argument, but there are arguments to counter that. If it ever went to tax court, which I doubt it will, it would be interesting to see how true valuation experts will chime in on this.
There are logical arguments on both sides here, which just proves that it's a complex issue and so it's very unlikely to ever be pursued in court. Those who would argue that it should be taxable would need to take the risk of setting a precedent that could have outside ramifications.
Personally, I agree with Dan that it should be treated as a rebate and reduce the basis in the item you purchased to qualify for the rebate. Which would mean that in the case of money-making MS you could argue that ethically you should be reporting taxable income on the excess after the basis is reduced to zero.