The flipside I think, is that if your group rejects optional rules presented, maybe there's a good reason why? I don't think players reject more difficult rules simply because less difficult rules are the "default".
Put it this way, let's say the PHB, instead of presenting a default for carry capacity, simply said "you can use 15 x Strength pounds, or you can use these Encumbrance rules". The players are still going to choose the option they like best, whether it's considered "standard" or not.
Your argument seems to be that the fact that one system is standard somehow gives players extra ammunition to defy the DM's wishes. They don't need extra ammunition, they can always simply choose not to play in a game they don't feel is fun for them.