Well, my Wight has this feat. He needed a such and such base attack bonus before he could select it. I look at Improved Knockdown as a sort of greater version of knockdown, since the character became better at "Knocking people down". Whether it's bull dozing them over, tripping them up, or setting them off balance and blowing on them.
Far as I know, no monstrous templates get Improved Knockdown. It's something that comes along with feat progression. Much like Toughness or Improved Power Attack.
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Slam Attack. Wights and Vamps are actually supposed to be pretty good at slapping you around, but let's face it, they took the feat because they can spam it. Much like the Non Monster PC's. Hell I've never been on a server where IKD is used so prevalently (more of an IDA guy myself, all the Zorro movies as a kid). You see it in a lot of PvP since pretty much it's the easiest way to keep folk from Transition hopping (using superior transition time to make an escape, as opposed to waiting till the other person is on the other side of the transition with them), easiest way to keep people from using the Walk Backwards Combat Exploit, or HipS (Though Monster NPC's can still Hips if they get KD'ed, in fact it triggers it), Or in the case of One Trick STR Ponies, keeps you from carving them up into sausage.
My last Fight with Undead PC's, had the Melee-er firing off IKD like no tomorrow (Something which is Nigh Useless against Otto btw but if they wish to Lower their AB by that much in the attempt, more power to them). It's especially effective for the folks with SNEAK attack since they then get SA damage on a KD'd opponent, it's also a favorite tactic for their Slap you over run away thing or shoot and scoot to the nearest Transition thing.
In short, it's just a feat, like any other feat picked up by anyone else. It gets used the same way everyone else uses it (just harder to use it against them due to the insane AC's some of them have) There's a very EASY IC way to address the issue though if you are interested. I wouldn't worry about it because the Justification for it is like you saw and when folks feel justified about it for whatever reason there's no getting around it, just turns into a big stinky argument. best way, is to handle it ICly the way that you would do so, per your PC's motivations.
~Rex
