I highly recommend you google kitchen scale - there are numerous reasons to use it and yes the people I know that have them do care about grams.

As the son of two cops and the brother of one, trust me I understand exactly how cops operate. I understand that they look at the collective scene and put everything together to make the strongest case possible, now that might not stick because prosecutor determines what is realistically part of the case. If a cop finds a kitchen scale in the kitchen, then they will still potentially include that as part of the charges and let the prosecutor decide if it's relevant for the case. Clearly the prosecutor didn't feel like either the gun or scale came into play, so the charges got dropped.

Instead we have people on here pretending to be prosecutors on Law & Order and making huge assumptions the weed, scale, and gun are all sitting nicely on the table next to each other.