SATA is based on PATA standards. The packets are basically the same. The v1.1 spec says on the first page that the basis for it is ATAPI v5 standard.
The first difference that it introduces is the way data is transferred through cables (serial vs. parallel). Since all of the sudden humanity can make serial transfers more efficient than parallel ones, this results in more bandwidth. The second plus that it introduces are thinner / more manageable cables and the third is a handier power connector which also provides 3.3V power to the device, although this is currently unreliable since many manufacturers simply include 4pin --> sata power connector converter, which of course does not have the 3.3 voltage. Suma summarum, the standard was pushed purely because it offers more bandwidth (and has a much higher potential to even increase the difference in the near future). Neater cables are just a bonus.
SAS uses the same electrical signal transport protocols as SATA resulting in thinner cables and more bandwidth. It's packet protocols also support SATA (among other things) so AFAIK there should be no problems plugging a SATA drive into a SAS controller.
Edit - to answer to the OP: WD used the knowledge they had from their SCSI line in an enthusiast product. These drives are rather expensive to make and the market for them is very small. I guess the other major players didn't go for it because they don't see much profit in it. I doubt Raptor drive makes much direct profit for WD either, but it certainly is a good marketing tool, if nothing else.
Rotational latency:
5400 RPM 11 ms
7200 RPM 8.3 ms
10000 RPM 6 ms
This latency is for one full revolution, so you can halve it to get an "average" time the disk takes to reach the designated sector on the target track.
As you can see, the difference between 10000RPM drive and a 7200RPM drive is only 1.2 ms. This difference can be overcome by using a faster / more precise actuator which actually even shows on the newer 7200 drives vs the original 36GB Raptor. Given a small enough partition, they tend to be even faster than the Raptor despite the 1.2 ms average headstart that the Raptor has.