You could plug in 1000 10 1 and the reforge results would be the same as 2 1.5. 1. Stat weights are more to establish the priority and do item comparisons. Once you have it, the values don't really matter so long as they fall in order.
---------- Post added 2013-01-21 at 11:29 AM ----------
I actually don't like using FD for stat weights. It tends to over-value haste due to averaging.
indeed. the only place where stat weights might matter if you're so volatile with your hit and expertise caps that it's uncertain whether you should be slightly over or under your caps, and what stats to use for that. but that's like 0.1% DPS difference at most whether you should reforge haste or mastery in most cases. I remember back in WotLK rawr days, my paladin could get 0.1% DPS from changing gems around. you're likely to gain more from playing better.