It's totally material if the "13 year old" turns out to be 22. How is the state gonna prove its case if they can't even determine true age? How is the state gonna prove where the act happened. The members of the sect allegedly move around quite a bit. Just prove you were in other states or even country. There are kids from Canada that are being held. What if the age difference isn't that great and this is the man's only "wife". What if they are legally married in a state that allows marriage as young as 14. Or they give a sobb story about how they move to the state to get married but the change in the laws prevented them from being married in texas? law It's not all as simple as "try em and fry em" when you have no supporting testimony from the victim or her parents. All you need is one sympathetic juror to get an "not guilty" or a hung jury. Prosecuting these crimes is gonna be as difficult and expensive and the raid was wrong.
Additionally, you have the suspicious changing of the laws with media outlets specifically pointing out that the laws were changed with the FLDS in mind. If the "victim" was 14, that's a tool the defending lawyer might use to sway sympathy for religious persecution. Which is what this boils down to.
I think it's simple minded to think that this whole cult is simply created to have sex with girls what amounts to 2 to 4 years earlier than you would be able to any way. According to the bishops records the dreaded 50 something to 13 year old "marriage" was just as as much a bullshit allegation as the 16 year old abused girl.

There are large communities of polygamists right here in the U.S. Outlawing something that people can just "do" like live with several women is about worthless. All you have done is told people that they can't "get married". Big whoop. If you can find several women that are happy with you having sex with them and supporting them, legal "marriage" isn't necessary for a relationship. And from personal experience, if you can have several women that know you have other sexual partners and are just happy "to be getting theirs" regularly, if you add the stability and safety of that closed community to the mix, I can absolutely see those women being totally happy with that situation.
It actually reminds me a bit of the military in times of peace. No threat of death and everything taken care of. You just do your part for the community and everything will work itself out. Without the polygamy maybe, if any group of humans had a like minded collective system like this, it would be unstoppable. Self supporting, everyone working for a common goal. The leader is the lynch pin in the whole thing, and Warren Jeffs was a sicko bastard.