Seabourn's price is much more inclusive than is Cunard's. Not only open bars, but tips, caviar, stocked bar in your suite, a free shore event in one port and a service level that's unmatched anywhere. 160 staff to 200 passengers. The quality of the service, uncrowded ship and extras are what you pay for on Seabourn. No, people do not drink to excess on Seabourn, typically. They just like the club-type atmosphere of not having to sign for drinks and worry about who got the last round,etc.
The biggest difference is the small-ship feel--you know everyone on board quickly, are addressed by name the firtst day, waiters and bartenders learn your preferences almost instantly--and you can do things ashore that can't be done with hundreds and hundreds of people.
Suggest you check their website for some feedback from actual Seabourn passengers in the video "Virtual Theater."