I thought that had effectively always been the case anyway. DNA testing is apparently more precise than blood testing. However, for some time now, blood tests have been able to ascertain that in many cases, men could not have been the father.
I think it would indeed be in the interests of some children if some women could demand DNA testing. I still feel pretty uneasy about men being allowed to evade their responsibilities, whether they are the biological fathers or not, just because a DNA test ruled them out of being the biological father. If three men sleep with a woman within a certain time span, none of them has the right to choose whether to be a father or not - especially if they have not used a condom. In those cases, the woman is the most likely to be able to assess who should be the father. The rights of the child and of the mother should always come before those of the man - whether he is the putative father or the biological one.