Aging cider in bottles

This has been nagging at me for sometime. Why is it that with high alcohol, bottled cider (or mead) for that matter it is recommended to let it sit in the bottles to age for sometime to "tame" it?

If the bottles are sealed, how does it lose any of the alcohol strength? What is the theory on why it mellows out?

Especially if the cider is carbed, and the headspace of the bottles is relatively non-reactive CO2 how does sitting help?

Is it really just melding of flavours?

I haven't done a lot of ciders but my experience is that the alcohol sharpness mellows quite a bit over time and the cider becomes more flavorful. It doesn't loose any strength, it just mellows. I recently had one that was very harsh when it was green. A year later, it was fantastic. The aroma was all apples instead of alcohol.

I like to think of it like leftovers. Sometimes the first night its good but a day later its awesome. I think given the time to rest all the flavors maranate and become great could be me and I'm probably wrong but its still the way I like to think of it

Lots of things happen. Some of the harsher, stronger-tasting compounds break down over time, and allow more of the subtleties to come out. No ethanol is lost; it's quite stable. In the case of cider, I especially notice a reduction of acetaldehyde (green apple flavor, can be overpowering in a fermented cider), acids, and a a bit of tannins over time.

It is true. I ferment a batch with EC-1118 and it was quite harsh at first. It did mellow out after several months, but the acohol content could still be noticed.