That was actually my concern about moving to nVidia chipsets. It's good in the short term, but in the future they'll probably have to move back to Intel.
By now, I'm sure most people are familiar with Nehalem having an integrated memory controller and QPI links instead of the FSB. But that is actually for servers and high-end desktop. Mobile and mainstream desktop processors won't actually have a QPI link. FSB and QPI are designed to provide a fast link to the northbridge where previously the memory controller and PCIe x16 links for the graphics card was located. In mobile and mainstream desktop processors not only will the memory controller be integrated, but an IGP and the PCIe x16 links will be integrated too. Meaning that there will be no northbridge and with no northbridge, no need for QPI links. (The other use of QPI links is to connect to other processor sockets which don't exist in mobile or mainstream desktop platforms). All that is left will be the slow DMI link to connect a southbridge for peripherals.
Based on this, there won't really be any future nVidia IGPs, since processors will already have an Intel IGP, and there isn't a northbridge to hold a separate IGP. It may well be a good thing though since the focus would then be on low-end discrete GPUs, which may not be glamourous but is still a step up from an IGP.
In this environment, Apple may well not need either Intel or nVidia to provide a southbridge. Apple and PA Semi may not have the time or skill to produce a full chipset, but they could make a southbridge if they wanted too. It may well be to their advantage to make there own southbridge anyways in order to integrate precisely the functionality they need. Things like the ethernet PHY and firewire which are currently separate chips could be built-in. I believe Apple's touchpad also uses a separate controller chip to assist with the gestures so that can be integrated. Things like better hardware Core Audio acceleration and other unique Apple technologies can also be integrated.