The problem shown is highly variable frame times, which translates into a jittery, inconsistent feel in a game. Tech Report have a superb article
here and were responsible for pushing this issue to the fore.
Average frame rates are just that, an average of data over time. Relying only on an average hides significant performance problems that players can feel. Games that have frame time graphs like those posted feel nastier to play compared to one with more consistent frame delivery. This is especially the case for quick games where you control the pov with a mouse. Try playing the D2 beta on "high" and see if it feels better.