Wow... so people are happier in the 4th & 5th books, when LV has returned, than in the 1st, 2nd & 3rd. Funny..
Joking lol. But it is odd, and in my opinion I don't think everyone has just been hit with a Cheering Charm.
i think that the teachers dont take away as many points in the first and second and third, etc. books because the students are younger (11 and 12) and they dont know any better at first, and just taking away a few points might get them to "mend their ways". Also, as Scellanis said, it matters how many times they have been caught before.
Couldn't have said it better myself really. I guess that sums it up. Maybe JKR just needed to do it to keep the story more alive or somehting, but nah your right I think.