i would recommend glassing them.  it really improves the impact resistance of the part and helps to ensure a consistent, even-thicknessed epoxy layer to ensure that the pieces are properly epoxy-coated/water-proofed.

they are also relatively simple pieces to glass so its not a lot of work.

can't really answer the question about 'most of chesapeake builders'. original kits didn't even provide deck glass.  then it became standard.  the hatch construction also changed a bit over the last 10 years...each time, in my view...slightly improving.

my sense is that the folks at CLC get a lot of feedback on how their kits perform and upgrade/improve their kit and building recommendations over time. 

Last year I built a 17LT and I did not glass the hatch covers or cockpit rim because the directions did not call for it.  I just covered both with a couple coats of epoxy then varnish.  The boat is holding up very well despite heavy usage.