Hi Uncle Dave,
The KC500(Roland) should seem heavier than the 450's (Mackie) because they "are" a bit heavier. The KC500 (weighing in at 59 lbs) is actually 8 lbs heavier than the 450.

The Roland keyboard amp I use is the KC300 (38 lbs)which is substantially lighter than the Mackie SM450. The SM450 is a bit heavier than I want to deal with, but I'm glad to hear that the unit is both well "balanced" and designed with handles on both the top and sides. The KC300 is relatively light but carrying the unit (via its' handle) is still rather awkward. Because the unit is more or less a rectangular box with 90 degree edges and corners, these edges and corners tend to bang into your knee/leg when attempting to carry it by it's top handle. This looks to be not a problem on the SM450 with its' rounded corner/edge design. I realize that when evaluating a piece of equipment for tranportability that it isn't only the weight, but that you must also take in to account the weight "balance" (center of gravity) of the unit and overall carrying ease as well.

This also brings up the point regarding 76 note vs. 61 note keyboards. Because 76 note keyboards are longer, it is more awkward to transport because of of its' greater length. Also, some keyboards have the majority of it's weight focussed at "one end" of the keyboard which makes it even more awkward to carry.

Scott