The difference won't show too much on new discs. It will show up as the discs wear in, more so in DX and pro plastic than Champ. Lighter discs begin to turn over sooner in their lives than heavier discs.
Yeah, i bought some random discs, I see the leopard is 147 grams.. i was like that cant be right, so weighed it on the kitchen scale, it was 146 grams! I then proceeded to weigh every disc in my bag, and every disc was 1 or 2 grams heavier or lighter than what was written on the disc.