I'm hesitant to jump in here since it seems the waters are chummed and full of predators. Then again, I really don't give a tinker's cuss who disagrees with me or for what reason.
I have my own 'policy' on watches and water resistance that I'll state up front, everything else is beyond that is in response to what's been posted previously. This policy is based on reading multiple manufacturers' recommendations (after all, no one sees more watch failure modes than they do), my engineering background and a lifetime of being in, on and under the ocean.
1. To answer the intial question: I think 50m WR is fine for a 'sports watch' - swimming, diving, paddling, hiking, sweating, etc. That's what I would tell the person seeking our advice (who hopefully is not reading this). 50M also happens to be my minimum WR rating for a field watch, since it should be able to be hiked, dived, rained on, immmersed in a stream crossing, etc.
2. If I know I'm going below the surface (spear fishing, skin diving, etc.), I'll wear a 100-200m watch - never a 50m watch. I'd go without a watch before taking a 50m watch to depth.
3. If I have a rig on, and I do wear a watch when diving (along with a computer and a backup computer in a pocket), then I'll wear at least a 300m watch. The exception would be one of my Citizen Aqualands, which are often rated to 200m. Since they are purpose-built dive watches I'll push the envelope.
What are my other considerations? Time since the last service/seal replacement, price and replace-ability of the watch, type of dive (pass diving in Rangiroa is quite different from a reef dive in a lagoon) and how much I
care about the watch. At one time in the past, I had a ladies Timex Ironman that I used for about 2 years (7-10 workouts/week). I cared more about that $20 watch (actually free - I found it in the ocean) than I do about some of the 4-figure watches I own now.
The fact that
most sports divers only dive to 130' is irrelevant, IMO.
Most people think a watch is solely for telling time! And
most people think they'll never go below 20m when they first learn to dive. Then two years later they're advanced open water divers taking a Nitrox class and glancing longingly at a Draeger.
Firstly, there is plenty to see at 130' and below - there is an entire U/W exploration society dedicated to researching the 200-400' depths, which is entirely reachable with SCUBA units. I bought and got qualified on such a unit last summer. It cost less than a Submariner, so they're not out of the reach of 'civilian' sport divers. Narcosis is a relative risk, not an absolute one. Similarly for DCS. Plan your dive, dive your plan and you'll be safe.
Secondly, the time you
most need your watch to function correctly is the time you accidentally break your dive plan and exceed your floor! It happens every day folks.
How people have sucessfully abused their watches is also irrelevant. Everyone knows someone who "never had it serviced in 23 years and it's still +/- 5 secs/day". So what? Does that mean it's the correct way to treat your watch? Should you really abuse a piece of equipment your life depends on?
Of course the manufacturer's are conservative in their recommendations - it would be irresponsible to do otherwise!
Of course watches intended for extreme environments are over-engineered. Part of that overengineering is purely a safety margin, part of it is to take into account the fact that the watch won't be serviced on the recommended schedule and part of the overengineering is to take into account
materials defects - not every part of every watch is delivered in spec. Some pieces (cases, for example) are expensive to inspect for defects. Much cheaper to overengineer the case so that when there is a void in the steel you still reach your spec - without having to x-ray every case.
Just my 2p, not trying to stomp on any feet. I don't know why depth ratings (and HEVs) generate so much passion, it's really pretty straightforward. Anyone for a Rolex thread?