I don't know how their hair can be healthier either since all the bonds in the hairs are broken so the hair is weaker. Maybe some women have a really hard time with detangling their hair or they use way too much heat and so when they texlax or relax their hair, they can detangle their hair easier and they use less heat which causes less breakage.
I am really looking into the keratin treatment now. I just don't have the money to get it done professionaly. I will read some diy forums and see their at home experiences!