It was an article quoting Nikkei, but that's paywalled to I can't see the actual report. I think it was comparing the 14 Pro (128 GB) to 15 pro (256 GB), so it's more in line with what you're reading with 256GB this year costing roughly the same as 128 GB last year.Which component costs breakdown are you looking at, out of curiosity? The one from the Japanese newspaper? They're all guesswork to some extent, but it's interesting to see that some think that 256GB costs less than 128GB cost last year. There's a suggestion that the price difference between the two sizes right now is under 50 cents. That's hilarious if true. Selling consumers something for nothing is the ultimate trick.
Perhaps 128GB saw a similar drop this year, so what I said above may not strictly be true in a 2024 to 2024 price comparison, but based on what I've seen from experience is that once you go small enough all the prices lump closely together anyway.