I notice my neighbor is adding a light blue plastic pipe at the foot of his retaining walls. Is this different than regular PVC drainage pipe?

Could you be speaking of a blue SDR 35 pipe.. see image?

If so, this is an exterior drainage pipe used by many municipalities to run sewer/drain pipes to within 10 feet of a building... has an increased flexibilty (not so brittle) and has a gasketed seal which allows for expansion/contraction/ground movement... ;)

Closer than 10 feet to the building and the sewer/drains belong to the plumber and he transitions from the SDR 35 pipe to regular PVC and brings it into the home nowadays... ;)

Questions? Let me know...

Mark