I have a soft copy of the 2009 brochure. Every 2009 model (not just the 2551), the couch is all by itself in the slide out.
I think you are right Waterdog. If my memory is good, the 2010 was the first year of the current-day slide out which has the fridge included. Unfortunately I do not have a 2010 brochure. Phoenix did not publish a brochure for every model year.
To make the "moving fridge" work, the furnace was relocated in some models over to the passenger side. I know the 2350 has the furnace under the bed since, which reduces the size of the under-bed outside storage compartment, and the loss of one kitchen drawer to accommodate a heat register. As is always the case, there are pros and cons to every deviation.
I have soft copy brochures for 2007, 2009, 2012, and 2015 model years, in PDF fashion. If anyone wants one of them, just email me your request. My email address is in my profile.
Ron