I ended up getting the email adress of someone at Novara bikes and asked them about the drive train. I was emailed a very thorough response. It involved testing all kinds of shifters and derailleurs and contacts with Shimano and compatability, etc, etc.

To make a long story short . . .

REI decided that the option of using the MTB rear derailleur was best made at the shop level and not as the OE (original equipment) specification. The mechanic and customer could discuss the pros and cons of modifying the drive train based on individual needs and comfort level.

He did say that they do have LX rear derailleurs and 11-32 cassettes available to send free of charge to customers who opt for a lower gearing option.