[jljljl]

This argument would explain slower sales or lower revenues, but I'm not sure this has much validity in explaining the lower net profit or gross profit margins.

Lower gross profit margins are probably better explained by either downward pressure on prices or upward pressures on costs of manufacture. It can also be driven by changes in product mix (e.g., higher sales of the lower margin iPad Mini). It's not unreasonable to attribute this to greater competition from lower margin Android products.