I don't think there is a "physical world" analogy that perfectly captures the situation where one company purchases advertising under the name of another company.

There are two problems with your coke and transformers analogies. The first is that you are using those words in a context where the trademark has nearly become synonimous with a category of things. People, particularly in the south, think of pepsi as being "a kind of coke" instead of a kind of cola or pop. The situation I'm referring to does not have that aspect.

The second problem is that in neither scenario does the competitor (pepsi or gobots) pay money specifically to have their product categorized under their competitor's trademark, and I think that is a significant difference. Pepsi cannot print "a kind of coke" on their labels, and they cannot print up signs that say "coke" and ask their retaillers to put those signs next to the pepsi display in their stores. This is dillution at best and it is illegal.

RE: Google's broken Trademark precident