I have really noticed that fathers are marginalised in a lot of ways. Our DS is only 18 mths but even so, all the nursery rhymes/playgroup songs only ever mention "mummy".
I also totally agree that it's because of the maternity/paternity leave thing. Men should have the right to have 6 months off as well. The only difficulty with men taking an equal part of the childcare from day 1 is breastfeeding, but even there, it's possible to make it work.