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I would not call it an oddity, I call it ease of fuse replacement. With only one junction block, you solve three big problems.
One, which junction block is the fuse in? With only one block, there is no question.
Two, ease of access. Very easy to open the hood, pop open the cover, and there are the fuses in plain sight.
And three, the weakest part of any wiring harness is the connectors. By having the main wiring harnesses going to one junction block, there are less connectors. The H3 junction block has three internal layers to make connections.
GM is starting to do this on many of their other vehicles.
The only drawback is for tapping into fuses for internal items such as radar detectors, XM radio adapter units, etc. This makes it necessary to run through the bulk head grommet, drill a new hole, or tap into a wire.