I feel you on the Legacy thing. I never got beyond Gen 5 before and now that I'm doing Alphabet/Apoc/my own spin, I'm finally on Gen 9. If it's not satisfying your play style or "needs", modify it or ditch it.
As for the puppy/kitten thing, I've definitely noticed that fortune sims tend towards those wants and that they prefer one or the other. Kids seem to be a bit more scatterbrained. Hardcoded? Not sure.
*points down* Pescado says no, so I must have just hit a statistical anomaly with these two. Sheesh. I took the heir's sisters to college last night and got them through because I couldn't stand the damn kitten/puppy wants another minute.
I am currently reading your Alphabet challenge - I am up to Dusty. This is a really interesting idea! I had not come across the Alphabet challenge before.
PS - I saw your house! The one you posted a picture of when I asked a previous dumb question! That just tickled me, I don't know why.