Well there are so many unkown parameters in there so our speculations are actually a bit ridicolous.
Just a few details, such as the edram requiring an uncommon potentially more expensive process, the Cell being a standard component could help bring the price down through higher production volumes as weill
Then we have all license fees, we just don´t know the size of:
360
Xenon - IBM
Xenos - ATI
EDRAM - NEC
DVD - ?
PS3
RSX - nvidia
Bluetooth - Bluetooth consortium (probably dirt cheap chips through some Sony-Ericsson deal)
XDR/FlexIO - Rambus
DVD - ?
The most tangible feature is the standard harddrive of the PS3, but as long as no one can show me proof that the core unit is the most sold SKU (or close to), then I think that is a moot argument.
Downloadable content will continue to grow in importance for both the 360 and the PS3, which will make the 360 core model an even more unattractive deal in the future.
I am pretty sure that if MS had known Sony would make the HDD a standard feature, they would have done the same thing, but that was one of the cards that Sony kept close to their chest until spring last year.
I agree in general that there are many unknowns. I feel pretty safe though assuming ps3 will always have a higher BOM for their core.
Two things:
1) MS pays no licensing fees for their gpu or cpu. They are paid in full designs completely owned by MS. The only license fee for xb360 AFAIK is DVD playback.
2) Core will fly off the shelf if marketed right.
Let me give you a few examples:
"Xbox360 core bundle with Halo3 for $250" next Christmas.
"Xbox360 core bundle with GTA4 for $250" next Christmas.
"Xbox360 core bundle with Forza2 for $250" next Christmas.