I don't quite remember what the quiz questions were in the german version, but they were mostly based on puns or riddles, so making the pictures easy to understand would probably be very important, as to not confuse the player.
For example, the golden frog probably had a riddle related to the Frog Prince fairytale, and having another frog might take away from that, since the frog prince only had one frog in it. So removing the other frog would make the riddle easier to get.
As for the chicks, maybe it had something to do with grammar. Like maybe the answer required a singular, rather than a plural or vice versa.