Wouldn't the same arguments be true for walks? Other runners don't advance, and they are not as valuable as a single. This is why I feel some people overvalue players like Gabe Gross. His OBP is okay because of his BB numbers, but his average still stinks. A walk is only worth ~2/3rds of a single, but its better to count them and look at OBP than use BA and not count them at all. And of course you'd rather have an OBP made up 100% of batting average, but it would take a fairly large difference in batting averages to make up for even a small difference in OBP. And OBP really is just what it says - how often a player gets on base. It does not attempt to assign a weight to how the reach base. So that's why you add in the SLG, which does assign a weight to the quality of the players hits, and despite still ignoring the difference between a single and a walk in the OBP component, it correlates 96% to scoring runs. And if you think about that, a hit is counted both in OBP and SLG, while a walk just helps OBP. So in OPS, a walk may actually be undervalued.