It certainly proves that ethical consumerism (if that's what this is - which I'm uncertain about) CAN change things. In this case, just small things, but I don't think it proves that ethical consumerism CAN'T change big things, too.
And I think there are plenty of examples of how consumer pressure, ethical or otherwise, has forced manufacturers to change. I can well remember how they were all insisting that a) tartrazine (E102) was "proved safe" for kids, and that b) "nobody'd buy orange squash that wasn't orange"...but consumer pressure means that E102 is now pretty much a pariah amongst food additives. Same goes, to some extent, for organic food - a fad, yes, but one that consumers have been able to demand and get.
Fairtrade chocolate's another one. And I'm sure there are tons of examples I haven't thought of.