I did this too. I registered for the same things at a couple of different stores, then I checked my registry online, and if something was purchased from one store, I took it off the registry at the other store. We also registered for normal things, but a few big ticket things, too- some people went in together and bought us big items (no projection TVs, though!!!).
Maybe they don't know how a registry works?
For example- a coworker of mine recently got married, and beforehand she registered at 3 different stores. She had me look at her registry and I flipped!!! Her fiance thought it was a good idea to give people options on what to buy you- so they registered for several of the SAME things on EACH registry:
i.e.- three different toasters at Bed, Bath and Beyond, and then two toasters at Macy's. Two blenders at Target and 3 different blenders at Macy's.
I told her, "You're going to get 5 toasters and 5 blenders woman!" She had no clue, and obviously her now DH didn't either. SO, we fixed it. I'm happy to report she did not end up with 101 toasters or blenders.