I understand what you're saying but I think you have got to draw the line somewhere, otherwise the weather - and what it can do - will become as letiguous an area as the risk of climbing a set of ladders is at work, and you'll be issuing warnings for every windy day.
The chances of anyone on a lilo hearing or heeding that warning are slim, and short of them seeing a red flag on the beach they'll still do it.
I can imagine there are plenty of people sailing/canoeing around the lochs and coasts off northwest of Scotland at the moment, but I don't see yellow warnings issued for the likes of them for similar conditions.
I can anticipate your reply - that's because there are tens of thousands of holidaymakers on the beaches of southwest England and only a couple of hundred up here!
Of course the reason they don't bother issuing warnings like that up here, is because whoever's responsible for issuing that warning is assessing the impact it will have, and up here it's small.
The line has already been drawn, and as you say it's not wind speed but the chances of someone losing their life.