You might have noticed that this thread is from 2012. Later, in another thread, I came around to Wikitree's way of thinking and handling this, and said so.
Using a woman's last name at birth made sense when genealogy was all done on paper, but with computer genealogy long established as the dominant force in the field, things have changed a bit.
If researcher #1 finds Mary Jones as a child with her parents, that person would search Mary Jones on Wikitree. If researcher #2 find Mary Smith with a husband and children, they may or may not know that the married woman, Mary Smith, is the same person as the little girl Mary Jones.
The way Wikitree does this allows her to be found under either name.
By the way, I know I wondered about this question before, but don't remember if I ever asked here, or saw an answer - Does the person search also find "Other Last Names"? That field is probably most frequently used for alternate spellings that may appear in various records. But it can also be used for multiple married names when a woman married more than once. I hope that also results in hits on the person search.