There's quite a bit of resistance, as the round is entering the chamber at an angle. Try chambering a dummy round without the benefit of the return spring to see what I mean. The round also has mass, and extra energy is expended to move the extra mass, thereby decelerating the slide.
As for your comment about pistols without a hold-open, less is better. If you sit there and repeatedly slam it shut without a cushion, it's going to accelerate the wear. Just like a hammer's striking face wears from hitting nails.
The OP didn't specify an action type, so we should err on the side of caution. The locking area in a 1911 is likely going to show wear. Take my Buckmark, for example. Closing it on an empty chamber has battered the surfaces of the breechface and the barrel, so I always manually shut it. We also don't know if it has cheap cast parts, like my brother's Davis .380, which developed a crack in the slide.
It's your gun and your money. If you want to beat on it, go ahead. But like the other fella said, it doesn't take much effort to do, so why not do it?
...but a pistol in no way is resting on the head of the case when it is in battery...
You sure about that? He didn't mention a specific pistol.