Thread depth on New Tyres -?

[Magnet]

It seems I’m out of touch with current tread depths as far as new tyres are concerned. 

Past experience had pointed me to expect that the tread depth was normally close to 8mm on new tyres, so I was a little surprised to find that the A3’s new set of Michelin Primacy 4 are measuring out at 7mm. 

This equates to a 12.5% reduction on expected, and if we say I previously hoped for around 18k out of these tyres, I would now expect to only get 15.75K miles. 
Or look at it another way:- Since the min. legal tread depth is 1.6mm, I now have less than 1/4 inch of useable tread. 

The other thing I notice is that the circumferential grooves are visibly wider than they used it be, so if you couple the two together, then there must be a fair amount less rubber used per tyre - at the customer’s expense - the customer now paying a much higher price for less! 
Anyone else have any recent experience of other brands? 
Kind regards,

Gareth.