Yes that's basically all correct.  The later T600's had a fewer other differences as well, but the grille is the obvious one. 

The T800W can fit the largest radiator of any of them.

The W900S stayed a W900 due to the axle placement, many get a little confused by it. 

The T800SH is the short hood model, very short and not rated for big power/big payload applications.

As for the naming, the Kenworth name came from Fredrick Kent and Edgar Worthington. They combined their names. This is also where the "K" and "W" come from in model names. K representing cabovers and W respresenting traditional long hoods.  I cant remember his name and cannot find the history article I read, but the "T" came from a later influential preson in the company. I am not sure if "C" came from the same or not but would guess it did.


To put it into picture perspective I found some pictures. At the end I attached a spec sheet as well for some of the trucks. 

T600A





T600B, earlier ones did not have replaceable fenders or turn signals at the back of the hood, a couple years had the rear signals and then in 97 they went to replaceable fenders.

 


The T600 was replaced by the T660 to accomodate the new emissions engines in 2007.  These are very distinguish able. Some people put mesh grilles in their T600s and can confuse some people who are not familiar enough with the KWs.

 


Next came the T680 last year. This DID NOT replace the T660, it was a model that bridged the gap between the T700 and T660.  Its currently the most fuel efficient truck. 

 




Below is a picture of a standard T800. You will notice many may look a little different. The Flat panel windsheilds have a more curved hood where the Aerocabs are more straight.  There is also a split fender model as well, but it is a shorter hood IIRC>




Then there is the T800SH or Short Hood





The T800H or high hood.





Then the T800W, other than its bold grille, the headlights are the obvious identifier on them . Not all T800Ws or T800H trucks have larger tires on the front.





Last month KW introduced the T880 which keeps with the theme of the T800 but utilizes the new cab that is used on the T680.





Then there is the W900. The first ones are coined the W900A by many even though that name came later after the B's were introduced. The W900A can be confused with the later W923 and W925s sometimes. The W900A also came in an extended hood version if your ordered the big motor (12v71 Detroit, KTA1150 Cummins, 3408 Cat).  First pic is short hood, second is long








The W900B was introduced in the 80s, the early ones were different from the later ones somewhat.  One thing that adds a lot of confusion especially to the W900 models is the Aerocab.  The hoods for the Aerocab are different from the hoods for the Flat windsheild.  With people being used to seeing aerocab trucks now, they see a W900B and see the hood is mostly flat and the W900L is sloped and curved. Then you see a non aerocab W900L and many people think its a W900B.  It can get confusing. Just look for the added spaced panel behind the fender and you will know.  The Fenders are different on the B and the L as is the grille.

W900B Non-Aerocab

 

W900B Aerocab

 

W900L Non-Aerocab





W900L Aerocab






And then of course there is the W900S








Hope that clears some of it up. Of course there is also the various C500 models which some people confused with T800s at times, the K cabover models, various other older models, the medium duty line, overseas models and the mother of all 963 shown in one of its various configurations in this picture.

 



 Here is a link to a brochure that shows a lot of the specs and configs of the heavier trucks.

http://www.paccar.com/paccint/Kenworth/WorkTrucks.pdf