I think you can GET a DNA test any time you want and contest father-hood if you choose. And the cases that say the child has an emotional right to have you as the psychological daddy even if you're not the DNA daddy are in the father's FAVOR>.. being that if you choose to continue ot have a presence in the step-kid's life, you can do so. Those "psychological father" cases were all about making it possible to stay in the kids' live by force if the mother doesn't want you, particularly since some states are also goign to require you to PAY for the kid even if it's not yours if you didn't question it's paternity early on.
Now, if you can find a different father willing to take on the burden of being the father... money and all... you are always allowed to give up your rights and let the other one adopt... I know of no court which will prevent a biological father from adopting his own child if there are no problems with the bio father (child abuser or whatever).
I'm glad though that it's becoming more accessible to find out for sure, through cheaper testing procedures.
I'd point out that the statistics for finding a number of men are NOT the daddys are skewed... as these are people who had cause to question whether they were the daddys... or else they'd not be getting the tests in the first place.
In most cases where a man and woman are married and have a child together, the dad's identity is not a question, so they never ask for a test and never get to be part of thost statistics.