Well, a high power to weight ratio facilitates faster work over a longer period of time. That's pretty significant for an aborist who spends a large fraction of every day running a saw. There's also the question of dealer support; it's problematic if the dealer who can fix your work tools is far away or takes a while to obtain parts. For us amateur firewood cutters, though, the pro saws are more fun than they are a necessity.
You make a good point, but I'll add that for those who depend on firewood for heating their homes, the advantages of a pro saw can make them the best fit for the job and not just more fun than they are a necessity.
If you have a longer heating season or heat a larger home, you'll need more firewood. Personally, I have little time to process firewood, so I need things to be as efficient as possible. In addition, I've used "farm/ranch" level saws with antiquated antivibration (290 for instance). The extra weight, vibrations, and longer time in the cut do take their toll on me during long cutting sessions.