Yeah, my impression is that both Sony and Microsoft spent a ton of money rolling their own last time, which is why both are going for more or less off the shelf parts this time around. BoM should be much lower this gen.
They're still using custom parts, and that will kill the early BoM, just like always, though probably less this gen than last. AMD probably gave them great deals, compared to getting something else made, like a SMP PPC470 SoC. IBM (and LSI?) are fat and full, while AMD is hungry for cash flow.
The real problem last time was that they used old methods and ideas, which were already patently bad, from the millenium-era resurgence of, "stupid simple hardware can go fast, you guys, so let's make all stupid simple hardware!" that plagued crappy RISCs. They were bad ideas from the start, their failures in implementation were well-predicted, and their supposed appearance in high-performance hardware was as a means to an end (neither MIPS nor Alpha, way back when, suffered from treating RISC/simplicity as a religion; it just happened to be one of the many ways they were able to improve performance, back then, with much more limited xtor technology at their disposal).
MS did a better job of it, overall, but neither had a CPU that was well-prepared for the memory wall, like our desktop and laptop CPUs were, and MS ended up using too little eDRAM to make the most of it (probably too costly to have 20+MB, at the time). The Cell needed a more powerful main CPU, a larger cache, and larger local stores, and MS' needed a larger cache, and eDRAM that was of greater capacity, and more flexible. With the long time between generations, not looking at it anew, and having cloistered server guys, and real-time embedded guys, helping the design, IBM/Sony/Toshiba made just the wrong decisions for the halo implementation. That left MS stuck with poor CPU core options, but they made what good they could out of it.
They don't just get a lower BoM by not going custom from the CPU on up, they also get accumulated wisdom from engineers who've worked on practical general-purpose CPUs, which the Cell, and thus Xenon's core, very much lacked. Either of them could afford the money for a custom CPU, but neither would have the capability to determine who would be good at managing such a project, without trying to poach a known quantity from their current employer

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