When they change the hard drive they just change the letter or last number like cech-Z00XY, changing either x or y. The same exact hardware with differing drives usually changes the Y and has the same X.
This one has a new Z, which is exactly what changed from phat to slim.
changing internal components (from a new manufacturer) would warrent a new model, but I've really got nothing here, it seems too early for me to accept another PS3 total redesign after the last one, but it could happen I guess
they could though redesign the PS3 and keep the $299 price point like the 360 slim launched
just to point out, the last PS3 redesign, Sony used Sand Dollar Enterprise to help mask their fillings of the upcoming PS3 Slim release
that's dated 18th August 2009, which is when the PS3 got announced, so E3 is a good bet that this is when we'll hear more about this, but if it is a new redesign, then why not try to cover it up again? (or is it simply not worth it for the 1000 people who search this hard for this info :P)