[v_london]

The main point of fragility I see with Apple that their profits mostly come from a relatively small group of people who live on the Apple ecosystem. Apple may have many product lines, but these products and services are mostly sold to the same group of people. If quality starts to degrade across the product line, or another company releases a killer product that's incompatible with the iWares, it's not inconceivable that Apple would start losing their loyal customers, thus lowering sales in all categories.

I don't see this happening in the near future since arguably Apple has never made better products than today, but you must understand that most of Apple's growth prospects come from them selling more wares to their existing customers than from Apple winning over new customers. In fact, I recently changed to an iPhone from Android, and the change was quite painful. The Apple store even called me back after sending out the order, wondering if me buying an iPhone as a new customer was a mistake (seems like that doesn't happen very often).