Good point about market maturity. If people are holding on to phones longer, sell them more accessories that people replace periodically, and make the base unit more also high margin (if they accomodate the official bumpers). But it's the consumer's choice -- they don't need to buy new bumpers if they are content with what they have. It's a variant of the razor & blades model.
All agreed. I'd add that the market is slowing down, so bumpers could end up bringing more profits. First, customers would be more willing to invest in higher margin products if the device was more robust and likely to last. And manufacturers could sell official bumpers with advanced shock-proofing, a nice metal finish, perfect fit to the case, many different colors, ...
