Well I have seen some bizarre complaints about the S9 having 'only' 4GB RAM, but I get what you're saying. However surely DIMMs are sold around the commodity pricing point so wouldn't be as expensive as they are if that were the case? For reference, 8GB DDR4 is ~£80 at retail so obviously less at the BoM level, and likely lower again for bulk orders. I know it's not exactly the same memory but ballpark £40 (4GB) vs say £20 for a high-end phone isn't disastrous, likewise for consoles, it's likely only making a relatively minor dent in the BoM pricing.
For discrete GPUs, like I said they're bound to increase in price if there's a shortage (it was predicted ~30% increase for the memory itself
last year), but miners being prepared to pay almost whatever retailers are asking is likely exacerbating the problem - supply/demand would find a more sane balance with gamers alone but as long as the market is supply-limited (Just to add to it,
IIRC GDDR production was reduced at least by some manufacturers, in an already supply-limited market, to make room for mobile/server memory) and no shortage of people willing to pay increasing amounts... Perfect storm? That also tallies with the cards unsuitable for mining being less impacted, though some impact is to be expected - demand is likely to increase from gamers unwilling to pay silly money for higher-end cards, along with the DDR pricing going up of course.
It's like the silicon wafer pricing hyperbole that was doing the rounds a while back. The reality is even doubling pricing there doesn't actually impact the final BoM all that much when you get to the final retail pricing.