UA100 notes:
The other is that the arbor is
removable. The latter is a mystery as Delta hasn't made
available any auxiliary arbors. It could be that they want
to Euromarket the saw in which case they'd outfit that model
with a short arbor so no one there can use a dado blade.

It's quite probable they're using some casting/machining set ups from
other saws. Several of the Taiwanese and Chinese saws have swappable
arbors, 5/8" and 1". Cuts costs to use old set-ups, doncha know?