MOCA and MEA over water???

V139 goes from southern NJ to eastern Long Island, cutting off the corner
of the coastline at New York, heading out about 40 miles over the ocean. I
just happened to notice that it's got MOCA's defined in addition to the
MEA's. The segment between MANTA and PLUME, for example, has a MOCA of
2000. This is 25 miles from the nearest bit of terrain higher than a
wavetop. Anybody have any idea why there's a MOCA defined?

There's some other strangeness with over-water airways in the area too.
PREPI is a waypoint 50 miles offshore (I assume it ties into the oceanic
route system). It's the intersection of V276 (RBV R122) and V312 (CYN
R100). What's strange is the MEA's along those airways.

V276 has an MEA of 1900 near RBV, then goes up to 3000 at D15, and 6000 at
D31. This is all perfectly reasonable, as it follows the floor of RBV's
service volume up with increasing distance from the station. What I don't
understand is why at D47, the MEA drops back down to 3000 (along with
another 2000 MOCA). How can reception get better lower down as you get
further from the VOR?

I'm sure this is all rather academic, since I don't imagine much flying is
done at those low altitudes that far out over the water.