Order Import for Invoiced Orders

Cross-posting this from the ticketing forum.

Is there a reason why the order import utility does not allow for the use of invoice payment method? The documentation says which payment method types can be used, but not why the types that can't be used can't  

It seems easy enough to tweak the import procedure to allow for invoice payment method, but I'm wondering if there is a compelling reason to not do this.

Thanks,

Sheela