:::About the diacritics thing (diëreses), I mainly do it because I don't want to waste a character on a hyphen and because the digraph "ee" has a typical meaning in English that "eë" avoids. I know this usage is dying a painless death... 
 :::Ehh. Chemically I would say that group 4 acts like a main group. Physically I am not sure. Sc, Y, La, and Ac are all soft and reactive metals with typically high melting points (that continue the in-period trend up from groups 1 and 2 pretty well, and also fall going down the group like groups 1 and 2). And they all have electrons relatively far from the nucleus like groups 1 and 2. Lu and Lr have electrons held closer and thus Lu behaves more like a transition metal physically (Lr is predicted to be like Lu). Sc, Y, and Lu are reactive but form stable oxide layers like Mg and Al; La and Ac's oxide layers are only somewhat effective in preventing corrosion temporarily. OTOH Ti, Zr, and Hf are all hard and refactory with high melting points and the oxide layers are all stable and they are all similar (no clear trend going down them). 
 :::Hmm...if you think of bifurcating groups, then you have a sequence Rb, Sr/Cd, Y/In, Sn, Sb, Te, I, Xe. The story still sounds OK, just not as neat. But hey, if putting multiple elements in the same slot is good enough for Mendeleev (cf. the iron triad and the platinum group metals), it's good enough for me -P 
 :::I personally consider it this way and think it's a good definition. What I am not suggesting is that it's the only or best version. I'm sure all the 3–11 and 3–12 people have their good reasons, like you do – it's just that I think mine are more convincing -P 
 :::And, well, putting group 12 in the transition metals is a 50-50 thing. So we really don't have much choice but to choose. The same with Sc/Y/La/Ac vs. Sc/Y/Lu/Lr. (P.S. The Haire book on the actinides uses the former but still calls Ac an actinide and La a lanthanide.)