Workers with families may actually be beneficial to companies. Why? Speaking as a parent in a single-income household, I would think they are less prone to job-hunting/switching frequently. It'd be interesting to see statistics on employee turnover rate for single vs. married vs. married-with-kids (or vs. single-with-kids, whatever). My income is very important to me, because I have three other people to provide for (plus associated "life" activities). It's stressful to not have a job; it's more stressful when you have a spouse and kids to provide for and, well, not starve, get into debt, lose your house, that sort of thing.
That said ... heh, 20 weeks is a lot, that's like 5 months. I'm happy with 2-4 weeks of paternal leave, but it's not a huge deal if a company didn't give paternal leave. I think it's great, because IMO, it's a statement of the importance of family and the importance of fathers in family life. I mean, I wouldn't complain about 20 weeks! But I can see how someone might think 20 weeks for a *father* is a lot.
Also, that said, 20 weeks for a mother is *not* that much. Even the official pediatric recommendation is to breastfeed, exclusively, if you can, for at least 6 months. It's really, really, really hard to exclusively breastfeed while working if you have any milk supply issues at all... because pumping just doesn't work the same. Sure, maybe companies should take that into account when working out pay, or maybe some of that should be without pay, or whatever, but unless we want to say to women that having kids is unimportant, or that making them healthy is unimportant, then time off for those critical months in a baby's development is a big deal to me. As a father. ;)