I know, I'm not certain why. I should drop a mail to their engineer to ask. But there's more electronics in the 1RBT naturally than the 1R, and not just the BT portion but also the DSEE stuff. So when it's corded we're assuming that it bypasses all that. The other thing is that at least to my ears, the padding on the 1RBT feels somewhat more padded than the 1R. Design-wise there are differences (woops! I forgot to put up pix of the 1RBT...later) and I do know that something simple like the padding can cause sonic changes. Similarly the porting/venting are in different positions too.
i.e. there are lots of variables in play that may cause the signatures to be slightly different.
IMHO, yes somewhat since I do believe the DSEE is being bypassed (despite what I said above, the operative above being "all" as bolded).