I'm sure there are chemical changes. I have air dried beech and KD beech and now both are on the order of 4 years old. The feel of the KD beech is different - it feels less dry even though I'd bet both have similar moisture at this point (the air dried beech is actually a little bit more waxy feeling and a little more resistant to planing).
The only other fully dry wood I experienced this with was apple - first apple I ever used was air dried (i got it wet - a pain to follow around until it was partially dry - just like beech). The wood had a very waxy feel, and then I bought some blanks that looked the same and were kiln dried. More musical and dry/hard feeling, even though both stored here.
I've noticed the subsequent movement (of several year old KD wood) in two places - guitars on fingerboards (flatsawn maple fingerboards gradually get some fret sprout over time if frets are flush trimmed - tiny protruding amounts of fret, even a few thousands feel sharp and snag fingertips), and in planes where i made my first planes with the irons flush fit down at the mouth. The irons gradually got tight in them and I needed to remove more wood. These amounts of movement go unnoticed, but both wood samples where I saw this were commercially kiln dried.
The baked wood apparently transforms much further, but only if heat is above a key temperature (something like 380-390 degrees F). When cut, it still has a little bit of stress - it's steamed according to the seller I get it from to make it more workable and less splintery, but when mortising the truss rod groove by hand, the little splitout at the edge of the mortise (well hidden by the fingerboard) is really unusual.
Lots of ebay listings of baked wood that advertise lower temperatures, but the studies that I read suggest that those samples are just more thoroughly dried and not as transformed.
Fret "sprout" is a common complaint on purchased guitars because most buyers couldn't pour water, let alone fix anything - I would guess that the reason it's not as common as it used to be is a step in the process where fingerboards are heated before being installed on a guitar.
I asked george about this for guitar tops (where older tops will often eventually shrink and crack, even though they are quartered), and he mentioned that he always put tops in the oven at a low temperature for a while before trimming them to size and installing them on a guitar (if they spring back a little bit after installation, no problem. If they shrink attached to bracing, some part will crack at some point.
Again, all guitar and tool related - no issues with furniture in 15 years so far (except for the one case piece where I glued the moulding end to end heavily, the miters open and close a tiny amount with the season - that's just the result of poor method).
The preference for makers in the past wasn't just to get commercially dried wood, but if possible, pay the premium for nice samples of decades old wood to get past the initial shrink and subsequent lesser springback. No clue if anyone has documented the percentage of commercially dried wood in year such and such. I would guess based on how much my moulding planes have shrunk over several years and then seemingly stopped, that the vast majority occurs in 3-5 years or so and subsequent amounts are minimal over any reasonable period of time - even for tools.