Those are very 'broad brush' figures, and are doubtless true (or even understated...) for some products or markets (a Picasso sketch, anyone..?), but the spread is far wider, I'd suggest. I ran a retail TV sales/repair shop for a few years, and margins were much tighter there than those quoted above; despite this, the big stores were undercutting to almost my wholesale price, so their margins were lower than mine, despite their higher overheads. I was involved in the manufacture of pool tables; there, too, margins were tight and competition fierce. I spent some years in a music shop; not much gold being dug there, either, and 10% off was a serious cut in profit, not easily given away. It's true that there are some commerces that have artificially high RRP so as to offer stupid 50% cuts, but they're specific, and not a generality, I'd say.
Just sayin'.