1) Intel sells a LOT of CPUs (and ethernet chips, etc.) due to mainboards which use ATI's chipsets. Intel would be shooting themselves in the foot if they said ATI can no longer make chipsets for their CPUs. Granted Intel does have other options (nVidia, Intel, Sis
).
2) Apple has gone back and forth between ATI and nVidia for years. The G3 iMacs had ATI video. Many of the G4 towers had nVidia (GeForce 2 MX, GeForce 4 Ti, etc.) while others had ATI (Radeon 7000, 9000). The G5 towers originally had all ATI (R9600, R9800) but one revision saw them go to nVidia (GFFX5200, GF6800) and the last G5 PowerMac line had GeForce 6600's. The G5 iMacs and MacBook Pros use ATI graphics. It's been a long-running flip-flop, so I wouldn't doubt it if Apple used nVidia cards again in their MacPros. If history is any judge, they'll come back around to ATI for the next revision.
2) Apple has gone back and forth between ATI and nVidia for years. The G3 iMacs had ATI video. Many of the G4 towers had nVidia (GeForce 2 MX, GeForce 4 Ti, etc.) while others had ATI (Radeon 7000, 9000). The G5 towers originally had all ATI (R9600, R9800) but one revision saw them go to nVidia (GFFX5200, GF6800) and the last G5 PowerMac line had GeForce 6600's. The G5 iMacs and MacBook Pros use ATI graphics. It's been a long-running flip-flop, so I wouldn't doubt it if Apple used nVidia cards again in their MacPros. If history is any judge, they'll come back around to ATI for the next revision.