I don't think focusing on R&D is exactly the right approach here - we know some companies may invest more on it, due to having hardware development (in Nintendo's case) and engine development (Nintendo, EA, UBi, among others) but I think you'd need to go to the financial statements and see the composition of the opex if you want to see what's the biggest driver of it. Personally, I'm betting on revenues - the game industry is heavy on human talent and the development of current games mean having huge teams - many of those in your list have opened studios in different part of the world in the last decade. It would be interesting to see how the opex increases coincide with building a new studio.
And as someone else brought that point, marketing will probably have increase its weight in relation to the total amount of opex - the advertising nowadays is a million years away from what we had in the PS2 era.
Well, yes, some companies invest more in R&D, some invest less, but if the question is trying to track cost of development, then to me it seems fitting to look at Research and Development and aggregate as best I can. Outside of being on the internal teams, it's difficult to point to specific sections and say "this has the greatest impact on revenue". Still, for sake of completeness, I've pulled those same ratios for the other OpEx groupings:
Which shows us that not only is R&D the biggest of these traditional OpEx breakdowns, it's also increasing at the fastest rate and with the greatest degree of consistency.
Now, I didn't want to exclude EBIT either, because it's a valid thing to look at, which gets us:
From which we can see that these companies have indeed become more profitable over time, although the chunkiness and inconsistency does raise an eyebrow. Still, those two views aren't in opposition; companies have been more profitable over time, but they're also spending more on development than ever before, which is growing - as a % of revenue - faster than other areas.
Edit: It occurs to me to be looking at medians too, since of course that gives us some smoothing, which reveals something of a switch:
(Keeping the same companies)
Which certainly gives credence to the argument that there are other areas besides R&D which are more expensive! And, of course, companies are more profitable. I don't, however, think this suggests that the combined process of making and selling a game has become less of an expensive process, just that companies are getting better with improving their margins. I expect it's the recent (last 5 years) push towards more digital/longer tail stuff, but that doesn't discount the increases in cost.