I think you missed the most important number: 1.5, as in 1.5 gb/s. I use an HP/Compaq NC4400 laptop at live music/dj/kj gigs. It's small (doesn't distract), powerful enough (2ghz duo) and cheap ($135.00). Drive speed is becoming important because I am starting to use softsynths. I'm stuck with a 1.5 gb/s interface. If I want to go the SSD route I don't have many options and so far the V4 seems to be the best and cheapest.
I suspect the V4 was actually intended for laptops with 1.5 gb/s interfaces and the only reason it has a SATA II interface is because it's a technological non-issue to do both. You can think of it as a "retrofit" design with a really good price. Given that perspective, the comparison with a SATA III drive is informative but misses the point.