I am a big fan of shot blocking, as well. Want to know my theory on why SB is more noticeable/effective in a zone?
SB is mostly used to defend drives...the players who drive the most are guards. In a man to man defense, guards defend guards and bigs defend bigs. In a zone defense, bigs defend drives from guards.
Furthermore, someone running a look inside offense (highest driving offense) will have most likely around 7 IS on their guards and double digits on the driving. Depending on which is matched up against SB, you can clearly see why zones are more effective under current training agendas.
Man to Man:
PG w/ DR 13 IS 8 vs PG w/ SB 4
3-2 Zone:
PG w/ DR 13 IS 8 vs PF w/ SB 12
The PF will clearly block more shots than the PG. It may be impractical to train PG to this level of SB, but I am confident you would see similar results in a man to man if you did.