I really would like to know why the 5D is left out in the cold here. Canon has the split and cross-split screens available for both the 1D and 1Ds. So it's obviously not a full-frame issue.I'd like to understand that, too.
I suppose it's one more way of differentiating the 'pro' line from the 'prosumer' line. The 5DII has two other focsuing screens available, the 1DsIII has 7 or 8, including a set that mask alternate aspect ratios (e.g. 4x5).