of those you posted, the centurion is the only one that looks like it was set up by someone who knows how to set up a bike. all the rest have very odd configs. look at the saddles, the position of the bars and brake levers. the centy also has downtube shifters, which are generally regarded as better and probably higher end components than stem shifters. also, no safety disc on the rear wheel.

to me this means the centurion may have been better cared for in terms of maintenance and possible upgrades.