If I were out of town visiting a friend or relative, and they wanted some free tree work done, I'd send them down to the Depot and get an 18" Wild Thing. It would get the days work done and then could sit in the garage and maybe still work if they needed it in a few months. If it sat for 6 months or better with fuel in it, still working would be lucky. Letting any saw sit for that long with current fuel in it would be lucky.
If they wanted a saw to cut firewood and general around the house work, that would last a life time, I'd send them to a dealer. Regular use with standard maintenance, will mean less overall maintenance, and a saw that will last. I have saws that were my Dads 40 years ago that will run, and out run, a lot of new saws, they're just heavy and vibrate more.
To the specific question, "is the exact same model saw sold at a box store different than the exact same model from a dealer different", I wouldn't think so. The dealer probably won't even carry the cheaper box store model, Joe.