That's what I thought too, and it held true for the base, but once you get to the top, the spacing for it to slide over the sides of the base accounts for laminate on both sides as well, so I had to re-cut all the pieces that go from side to side on the top larger.
starting on the monitor base that attaches to the cabinet base, then for all the back and top pieces.
I could be wrong, and maybe I mis-measured somehow (Though I don't know how, I'm a big fan of measuring 4x, then cutting once

), but if I DID somehow measure wrong, I would have had the same results for the base as well.
I agree the plans could use some help, there were a couple places they were missing dimensions :-)
Make sure you use the addendum for the final dimensions, there are much better drawings there.
To see if I'm right or not, try clamping together the base, and see how the monitor base the goes on top of it sits. That's the point I realized I messed something up.