I have installed maybe 10 or more MX-V radio sets and they where all factory binded.
However, all the other Sanwa/Airtronics radio sets are not factory binded.

I personally think Sanwa factory binds the MX-V set because of the fact it's a budget radio set and maybe especially suitable for novice users. I think they want to sell it as much as plug and play as possible, maybe to avoid any warranty claims that are just beginners lack of experience and skills, failing to bind their radio set the proper way.

Sounds reasonable to me...