I think you're right and at the same time wrong. I think many people view Club Nintendo as a program to get exclusive rewards, so naturally getting things you could have bought isn't desirable. However, I would say a fair amount of frustration comes from the fact people want physical items instead of digital items. You can look at people like myself, Conan and it's pretty clear that some people don't care for digital items in general.
I totally get that, and I share your frustration. I would have MUCH preferred a nice statuette or limited soundtrack to the digital rewards they offered this year. However, I'm trying to envision a scenario that would satisfy a Platinum member's desire for an exclusive reward while also working with Nintendo's limited budget. I think the lukewarm acceptance of the WiiU in North America (and the marked increase in the cost of shipping goods) has caused ClubN US to slash their budget for Platinum rewards. Physical goods like the Mario statue and pins are likely a thing of the past unless there is a dramatic change in sales. My DLC described above would be an inexpensive bonus for those of us who have the games and reached platinum, but this scenario would only be viable if offered in conjunction with a more practical but mundane reward, like the selection of digital titles.
I also want to point out that I would have bought all these games regardless of Club Nintendo. I don't buy them because I want to reach platinum; I buy them because Nintendo is arguably the greatest developer in gaming, that they consistently produce fantastic games and unique experiences, and that I got the games at a nice bargain due to the hard work and dilligence of the good people here at CAG. Platinum rewards are icing on the cake for me.