I have seen that on several dates in Feb. and Mar. I see the family bedroom selling cheaper than the bedroom on the Empire Builder. Why is this? Is it because of availibilty? Sounds like a good deal to me, windows on both sides of the train, but no bathroom which is not a big deal.
It's due in part to the fact that one doesn't see too many families traveling at this time of the year, so those rooms often go unsold. Additionally of course is the lack of the bathroom and what many would say is the less desirable location on the lower level, which leads to increased track noise. Some people are also turned off by the idea that each side only gets a single window, unlike the double paned window found in the bedrooms and the roomettes.
While I won't deny the convience of having the bathroom in your room, I probably wouldn't pay much more than 50 to 60 bucks extra for that luxury. And the family room IMHO is a nice room, I've traveled in it twice myself, although I really did have family in the room.