Well hmm, if it's set to always require (in other words, there's no option for us to turn on or off for this element) then it will always have a checked option when submitted right? I see a lot of forms as I'm sure you have seen our examples off all over this thread and such, that don't have this radio button that is already checked on default. Truly it's needed. A good example (not specific but...) would be:
I have 4 choices of a specific product's flavor, color or whatever (insert your choices here). One of them has to be chosen, but....
If it's prechosen for the user, then they may not always realize that they need to change it, they may just bypass that selection as it's already chosen and there's nothing to tell them different (such as an error stating a selection is required).
This means that they will get whatever default is checked. How do you get around that? Not everyone uses a shopping cart for their order processing or information gathering, and sometimes these radio button choices are necessary to include. If it's already chosen, then there's no way to make it "required" for them to make a choice correct?
Just trying to get my mind around why this is such a problem. Check boxes can't fill this option as you can check multiple boxes as a few people have already stated in a few other threads and that leads to issues so radio buttons are the option they need, but if it's already a chosen choice for them, it's very easy to get "mis"information if that option was overlooked since it's already picked and cannot then be required.
Hopefully that makes sense.