Denon's three digit line, e.g. the 988, were originally intended to be sold at big box stores like circuit city and sears. Their four digit lines were supposed to be carried by specialty retailers. The line has certainly blurred with Best Buy's purchase of Magnolia, which was orginally a specialty retailer.
There are some small differences between the 988 and 2808, most notably that they come with different remote controls. However the differences are few and far between, and for all intents and purposes, they are the same machine. Yes the 988 does not have the CI designation, but I bet it's still part of the feature set. It's unlikely that Denon wanted to remove this feature. The reality is, no one from a big box store is going to try and give you the kind of support the CI designation is intended for.
Just as a side note, Denon has always carried their 3xxx series receivers and up at specialty retailers and have never made a corresponding cousin with a three digit number.
Also note that Denon has long provided upgrades for their 5xxx series products. These upgrades were often expensive, costing $500 or more. It is unlikely you will ever be upgrading a Denon product other than their top tier products. It won't be cost effective for you given the price you intially paid for the unit. Now when discussing something like the 5805, which intially cost $7,200, well at $500 an upgrade starts to make a lot of sense.
