That has been a common misconception. We did a bunch of weights two years ago and posted them here. Even back then Flow was right in there or lighter than the other major high end brands. Those results:
Here are some actual weights measured on our shipping scale. For each this was a single Size Large binding with disk and all mounting hardware:
Flow NXT-FSE = 2 lbs 4.8 oz
Flow Quattro SE = 2 lbs 2.37 oz
Flight 2 Men's = 2 lbs 3.1 oz
Rome 390 = 2 lbs 2.32 oz
Union Force = 2 lbs 2.44 oz
Impressive! I'll be getting the NX2-SE. Thanks!