I think you may be exhibiting a regional bias with that figure about bonito shavings.

I'm not so sure that only 'upscale' restaurants make dashi from scratch. Saying that, miso soup doesn't exactly showcase a good dashi broth as the taste of the miso will swamp the delicate flavours. So, where miso is added to the broth, and where dashi is used as a cooking condiment, I agree, it is often the case that commercially prepared dashi (as a concentrate or powder) is used.

But it's not always to do with the perceived 'class' of the restaurant. There are many modest establishments that specialise in 'simple' dishes where the success of the food is almost dependent on the dashi making skills of the chef. This seems to be particularly the case with soba and udon. In many of these places, making dashi from scratch is more economically viable than one might expect as the dried fish can be re-used. Dashi made with first infusion tasting different to the subsequent infusion (niban dashi) which will have a different use (miso soup being a prime example).

I'm wary of generalising too much about what people eat in restaurants on this forum. Whilst I wouldn't expect Yoshinoya, Royal Host and Nakau to be making dashi from scratch, the experience of visitors to Japan won't necessarily reflect the reality of what's available. What I mean is that a visitor (certainly a Flyertalk reader) is more likely to be eating dishes made with real dashi than any statistics might suggest by following advice from guidebooks and concierges, acting on recommendations and by conducting their own research on where to eat. Even if it is true about the rarity of 'lower end' establishments making their own dashi, this wouldn't necessarily be the experience of a visitor with a real interest in Japanese food, even those with smaller budgets. It certainly hasn't been mine.

(Sorry about any perceived nit-picking, it's just that your statement could be viewed with unnecessary pessimism by those who can't afford to eat at higher end places)