[jwestbury]

> My theory is this: your favourite hobby store expands and adds one more aisle of fantastic products and five aisles of garbage. You’ll likely perceive quality as having gone way down.

This is actually something which is borne out by research, though in a slightly different context. Niro Sivanathan at the LBS has studied how arguments are presented, and essentially, recipients of arguments engage in an averaging function instead of an additive function, when evaluating strength -- adding one weaker point to a pair of very strong points actually detracts from the perceived strength of an argument.

It would not be at all surprising if we did the same sort of thing in different contexts, such as the example you gave here.