Just got back to this thread.
You have to remember that the original Toaster (2000) was being designed nearly 15 years ago, and the 4000 about 9-10 years ago. In 1990 a TBC was about the size of a small VCR. Even my TBC-IV, which was designed in the mid-90s is a full-sized card (and very densely populated, too). It would have been very difficult for Newtek to include the same functionality on the Toaster itself.
If all you are using is 'live' cameras, then you'd only need 3 TBCs for 4 cameras. The 1st cam would feed both the 1st TBC's sync input (genlock in on my TBC-IV) and Toaster input 1. The second cam would go to the 1st TBC's regular input. The output of the 1st TBC would go to the 2nd TBC's sync and Toaster input 2, and so on, and so forth.
Cam1 - TBC1 sync in - Toaster 1
Cam2 - TBC1 video in
TBC1 out - TBC2 sync in - Toaster 2
Cam3 - TBC2 video in
TBC2 out - TBC3 sync in - Toaster 3
Cam4 - TBC3 video in
TBC3 out - Toaster 4
