Well, RES is resident in physical memory. It just is marked so that the kernel can make reclaim it when it needs to. But until then it's resident. If you want to track leaks you need resident-and-in-use metric which may be more difficult to come by (probably requires scanning smaps?).

It's a case of people using the subtly wrong metrics and then trying to optimize tools chasing that metric rather than improving their metrics. That's what I'm calling misguided.