It's true that the SA bodies are different (slightly thicker) than the standard S bodies. I just calipered my SA160 (knock around travel guitar) and my S1520 and there's some difference, but not much. I played an SA1260 recently that seemed thicker still compared to my SA160. The trem (whatever they call it: SAT30-Pro or something?) was also different than the regular SAT30 on the lower end SA's.
It does seem like something odd happened with the simultaneous release of these two guitars. Here's a quote from an interview on the Ibanez Japan site (I printed it out so I could remember what pickups they were planning on using, but my printer cut off part of it, hence the ...):
IBANEZ: You are currently using an SA160 along with your signature Japan market AT 100... tell us what you like about the SA160.
ANDY: I'm most excited about the solid mahogany body. It's really got a tight focused (...). The signature AT100 guitar is more of a traditional alder body and maple neck guitar. The SA160 has more chunk and tighter low end because of the mahogany body and the great rosewood neck. (It) sparked my musical creativity.
And here's a quote I got from a distinguished Ibanez insider (who sometimes frequents this site): "The new AT will be an all mahogany body guitar following the SA profile. It has two Dimarzio Cruiser single coils in the neck and the middle and a custom wound pickup in the bridge... The neck is similar to the SA profile ... It has a regular SA type trem and Sperzels. Very sweet."
So I wonder what the deal was here? It seems like the early AT300 prototype was based on the SA and later it underwent some significant revisions. Maybe THAT prototype morphed into the SA1260, and they went a slightly different direction with the AT300. Most folks here think they misgauged the market, but I suppose we'll see if both models persist.
Anyway, I'm still planning on ordering the AT300 soon (once I part with a couple of other guitars), mostly because I really like the inlays, and I'd end up upgrading the pickups anyway. Plus (as I said earlier), I expect the AT300 gets a bit more love at the factory before they ship.
Hey VaiJem, maybe sometime you could check out the SA1260 down at GuitarX and give us a summary of the differences. I respect your opinions and would be interested in your informal review.