I agree that cartridge bearings are easier to install and don't require maintenance. Honestly, if I had a company mass producing bikes I would use cartridge bearings because they could bring down production costs not to mention be a great bullet point in marketing blurbs. Although I've never witnessed the effects of brinelling in c&c bicycle headsets (that still contained grease), the theory is sound and I could use it and other such theories to further promote the advantages of using cartridge bearings in marketing my product line.
Good quality cartridge bearings certainly have their benefits, alternatively so do good quality c&c bearings... IMHO it's up to the user to decide which suits him/her best. But of course poor quality cartridge and c&c bearings do exist and should be avoided altogether.