I feel a need to explicitly state some stuff that has been suggested in this thread already, but maybe not expressed in quite this manner.
Against tough opponents (WS4, S6 or better), Skinks and HW+S Saurus die at exactly the same rate. Against such opponents, Skinks actually die slower than Spear Saurus, due to the 6+ parry save.
You can get 2 Skinks and a point left over for the price of one Saurus. So, if they all die the same, your tarpit unit will wind up lasting twice as long if it's made of skinks. Plus it will be a lot more mobile and better able to engage the intended target, thanks to M6.
Note that this only matters if your strategy is to tarpit or redirect a powerful enemy unit. It's true that the Saurus have a better chance of actually winning combats, especially if they happen to be fighting something that's not too killy and that they can injure. They're also better targets for magic support, such as Wyssan's. But the problem with Saurus is that there are a lot of opponents they have trouble winning against, meaning their role is often reduced to just tarpitting an enemy unit while you wait for support to arrive. In those cases, its often more efficient to spend your points on Skinks.