> You're over-generalizing from a small non-representative sample
Sure, of course, everyone is posting anecdata. But I've also run with a lot of people averaging 50+ marathons a year and they're dismissive of the 300-400 miles claim for shoe life. I know one of them did well over 50 marathons in the same shoes, for example. I managed a 4:50 with year old shoes that had about 750 miles on (through running and walking) and no injuries.
I can imagine that if you're going hard, fresh shoes with cushioning and support are important, definitely. But most people won't be going hard, they'll be bumbling along for a 5-6h pace in their every day trainers.
> We're not all young and invulnerable running occasionally on the most forgiving surfaces in the mildest climate.
Kind of you to suggest that I might be young but I'm approaching my half century. Most of the people I've run with are the same or older. I will concede that South East England does have a relatively mild climate for most of the year.