I'm honestly not sure. It might have been changed during edits, maybe. The way the description is written it only talks about involving another person, so maybe we decided later that we needed a Level 20 effect and wanted to make that one more impressive. Or we needed to do that with at least one of them, maybe. All of the sample maleficia are pretty terse, but I suspect we were over our word counts. Sorry about that.
Without having read the Malefica in detail, perhaps the "victim" type has to match the "target" type - so killing a plant is enough to heal a different plant, but healing a human requires the death of another human?
That's a fair bit of extra flexibility (a spell that can heal plants, animals and humans), so I could understand the magnitude gain,
Of course, healing a human by destroying every bit of plant life within 2000 paces might disadvantage you at times too...
Then, because the main implicite question was: "do the guidelines with "victim and beneficiary" needs a +2 for "group" equivalent (because 2 "targets") called "victime"", the answer seems to be "No".
I like the maleficia more than before
Edit: Gareth, it seems the extra magnitude is for human => human (0), human => animal (+1), human => plant (+2).
i think the main target remains human because maleficium are inherently linked to the humanity (soul) and ability to sin.
As I see them, the maleficia are a way for a demonist to say: "I can heal you, my fellow king, but you understand, those powers need sacrifice, and i'll need your son ability to see the light... So I really can't help you, and i'll pray for your soul, because no father would sacrifice his son for his own sake...
Oh are you really sure of your point?
So be it, my king. you are the ruler, who am I to contradict your potent words? I'll do what you ask"