That "half-a-second" pause you are experiencing is not only a 4S issue, it is an all across iOS platform issue.
The reason why you get that short pause after you press the Home Button is due to Multitasking.
After tweaking, disabling, enabling features all throughout the phone for the past year, I have come across the fact that once Multitasking is disabled, exiting apps via Home Button is almost instantaneous. The graphical interface is much more smoother as well.
A side note, applications load slightly faster with Multitasking disabled, but, the tradeoff is that they won't stay suspended in memory.
As of iOS 5, I am no longer able to do so, because the dock becomes greyed out and unusable for some reason, so I just keep it on.
It's very weird why the phone acts in that manner because of the feature, but I'm sure anyone else who has done this can confirm as well.