What you're forgetting is that retail organizations (and large businesses in general) completely over-react to minor things. Your numbers make sense, and work on logic. A lot of businesses don't always do that.
Also, let's not forget the point of the promotion was to move $75 worth of OTHER LEGO SETS. It clearly goes against the spirit of the promo itself to buy the sets to get a free set, and unless every TRU manager is dumb, they are going to take notice. General employees may take notice. Other customers may take notice. There's something to be said for keeping a low profile.
They literally need to get one old fashioned complaint letter to get wheels moving. Or they look at their own numbers and see something is up. I know we all want to say that retailers (TRU in particular) are really dumb, but obviously they have some people doing their homework there, and that homework gets easier and easier with all the analytics and instant access to information.
The following retail changes have occured in the last 12 months alone, and this is a partial list:
1. Walmart has stopped their 50% off LEGO After Christmas clearance.
2. K-Mart.com no longer accepts (Many) coupons for LEGO.
3. Barnes and Noble coupons exclude LEGO.
4. Target.com has begun pricing their hard to find/retiring soon LEGO sets at higher than MSRP regularly.
5. TRU (most of them) have stopped selling their PROMO items separately, and are actually getting corporate orders to NOT sell them.
6. TRU Coupons (some of them) are starting to exclude LEGO.
I know I am not going to change anyone's behaviors, there are some folks who are short sighted and frankly don't care about "the future" of LEGO Investing, they want to get as much money as they can right now. I am not claiming you are like that, but there are lots of folks who are. Some on this site, many others who don't bother.
But to deny that the impact of increased LEGO reselling visibility/reseller actions helped bring about these changes is really silly.
I am not trying to take any sort of high road here or call anyone out, I am just pointing out that there is a cause/effect relationship between resellers and retailer policies.
I am not one of those sky is falling sorts, but anyone who wants to do this long term should think about their actions and encourage others to think as well. Lots of people have pointed out increased competition/lower prices, harder to find deals, etc etc. It's not going to get any easier from here. And we certainly can't be surprised when retailers adjust.