Diet does have A LOT to do with it! You're not going to get big if you don't have enough calories to support it; and on the flip side, the pot belly isn't going anywhere if you are eating too much.
Yes what you said was true... less reps, higher weights to gain mass; more reps, lower weights (that's not to be read as light as a feather - lower meaning you are tired by your 12th rep), more toned. However, the less reps usually means about 6, or even less if you are trying to max out. I believe the more reps is toning you because you are burning more calories in the process. Less reps is focused just on the muscle and how much it can possibly lift.
But ladies, stop worrying about getting "big" by doing weights. Our bodies won't allow it. Do the weights! Muscle burns fat!
PS Mike, your before and after pictures look great! What you're doing is working!