I can see that an HBP might have a higher run expectancy than a non-intentional BB. While sometimes guys are occasionally intentionally hit, it is probably more rare than a guy gets pitched to carefully and walked. There is more of an element of strategy in walks than in HBPs, so the outcomes might be slightly worse. As for 1Bs v. reached base on error, with an error there is maybe a greater chance of being awarded or taking an extra base. That's just a guess. I'm sure Tango has the right answer on his blog.