The OS isn't necessarily that much more demanding on the hardware than it was in 2008, rather the applications are. Also, people have come to expect a certain degree of smoothness in the ui which Android has been behind on - iOS just hides loading times with animations, so its always been perceptively smoother.
Its a bit chicken and egg; the developers add animations to the os to make it feel smooth but in the process they make it more demanding on hardware. Rinse, wash and repeat.
The OS isn't necessarily that much more demanding on the hardware than it was in 2008, rather the applications are. Also, people have come to expect a certain degree of smoothness in the ui which Android has been behind on - iOS just hides loading times with animations, so its always been perceptively smoother.
Its a bit chicken and egg; the developers add animations to the os to make it feel smooth but in the process they make it more demanding on hardware. Rinse, wash and repeat.