The only other way this 896MB of memory could make sense is if Nvidia used more dense 128MB chips, but only 7 out of 8 chips. It could still use 448-bit bandwidth. And the 1GB version would use 512-bit bandwidth with only 8 memory chips, like Radeon's HD2900XT (which would explain 9800GTX's incredibly complex PCB). Remember, there was a 256-bit version of HD2900 that used the same PCB as HD2900XT, so the 9800GTX could be as well using the same PCB design that will be used for D10U chips. If the codename is D10, perhaps Nvidia will actually call it Geforce 10000 Ultra or something like that.

I wouldn't be surprised if Nvidia did that just to up its stock value (that fell over 40% within the past few months---OUCH).