The ethical issues are really dependent on how the publisher runs the operation, since the conventional model, as others have pointed out, doesn't really assure editorial integrity anyway. (Despite all the dirt thrown against the wall over the years about long-term loans of gear, cushy relationships among reviewers and manufacturers, etc. I think most mainstream reviewers try to get it right. Whether there is an inherent bias to always say something 'nice' is another question, but I seem to recall some less than stellar reviews in magazines like Stereophile).
Why couldn't a site have a front end that is 'free' to users for capsule reviews and certain coverage, but a 'pay wall' for more in-depth reviews? Charge users a nominal fee for access per review? Like an iTunes charge- .99 cents? Not much, and those pennies add up. Advertising could still run on the 'free' part of the site to reach the greatest number of users. Frankly, while I skim most gear-centric websites and have an e-subscription to Stereophile, I rarely read whole issues or all of the reviews- just focus on the stuff I am interested in. And, eventually, the pay for access reviews could be migrated to the 'free' side of the wall.
