Suh didn't even get fined for that. No discipline at all.
I think the after-whistle-stuff that occurs face-to-face between players -- basically everything other than a legit fistfight -- is difficult to evaluate as suspension worthy. Typically these types of scrums lead to flags, and at most, an ejection; but few result in anything more than that. (Keeping it Miami-related -- McCain got tossed vs. NE for an elbow/punch after the whistle, but wasn't suspended.) I think that Suh play looks worse as a still photo; plus, there's the fact that he throat-shoved a skinny, white QB. If that's an OL, it's a flag, and it gets close to zero attention.
When it comes to defenseless players, however, suspensions seem to be more likely. Taking a shot at someone who is defenseless that causes injury and/or appears as though the intent was to cause injury gets much more league attention. In the incident with Gronk, as others have already noted, the Buffalo player was prone on the ground when Gronk laid the hit several seconds after the play. Had he hit him face-to-face, with both players standing, this isn't even an issue today.
Gronk doesn't have a reputation for this sort of thing, which also seems to factor into league decisions regarding suspensions. As a non-Pats fan, I'd be okay with a heavy fine and/or 1 game suspension. Anything more than that would definitely seem excessive.