Uncle Dave might well be right that it is just a matter of adjusting to different keypads. However, it also may not be the case that it is "simply a matter of mathematics". It is also a matter of ergonomics. A person's fine motor control may be more precise with weighted keys than with unweighted keys. Let us say that an average person only has sufficient control to distinguish 5 ranges of 128 velocity values when unweighted keys are used, but has sufficient control to distinguish 10 ranges with weighted keys. Then most people would be able to play more expressively (ignoring continuous controllers) with weighted keys. Note that it is because people do not have the precise control that midi offers that different weightings might allow different amounts of control.

Note that foot switches and foot pedals tend to offer much more resistance than keys. This allows our clumsy feet more control than they would have if they had the same resistance as unweighted keys. Likewise, weighted keys might make it easier for "clumsy" fingers to control the keys.

One other note. Weighted versus unweighted may not be the issue, ultimately. It might be unweighted keys with stiffer springs would be more subject to fine control. The main point is that it would only be a matter of mathematics if our fine motor control matched the level of precision offered by the instrument. I am sorry, this is probably a little to abstract to be of interest to many people here.