NCL is big on up sells but I haven't hear of Carnival doing it on a regular basis.
However, I wouldn't be surprised if this is now SOP. (Standard Operating Procedure). From a business perspective I could never really understand why you upgrade someone for free when someone else would be willing to pay a reasonable amount for it.
In regard to not going for the up sell you might be right. My first cruise was in a full suite, on Celebrity, and I was spoiled after that. Then again, if I had been in an inside or even an outside cabin I may have never cruised again.