well it seems they will have to add something, if the hardware is there why not enable it? I guess it could be a honeycomb issue. If the hardware is there, then I'm sure this community will find a way to use 4g (for free?)!
I hate when people post information without any sources... (including myself!)
I swear I initially read that you might need to actually send it away to Motorola, but I can't find that written anywhere now that I am searching for it. But this link says you could take it to a Verizon store:
Motorola Xoom will require hardware upgrade for 4G, software patch for microSD use | Android Central