Well, there's a catch. There is another difference after all - some of them have a different colored paper wrapper.
Nothing else is different, so it would seem to still make sense that you just pick 4 of the biggest. But for some arbitrary reason, society decides that, no, you can only choose from cupcakes with yellow wrappers. You end up stuck with a little cupcake because some of the big ones were removed for no apparent reason. How is that fair?