Thought I'd dive into this.
Bicycle brakes are designed for a mechanical advantage of about 4 to 5. That means moving one unit of distance between the pads requires about 4-5 units at the lever, the point where your hand touches it. If this number is much larger, you get a soft feel and the brakes tend to grab; much less, and they feel hard and it takes a lot of hand force to stop.
I experimented with this some time ago, using road levers with cantilever brakes and vice versa. It was pretty scary. The "hard" brake required quite a bit of force to stop, in fact, my full strength; the "soft" one was so hard to control that I wouldn't leave the driveway with it.
There is some room for adjustment of this effect in certain kinds of brakes. Especially cantilevers, and perhaps some center pulls, by adjusting the length of the straddle cable. All kinds of other things affect this as well, such as adjusting the pad position. But that's pretty minor.
I suspect that our tendency to mix different kinds of levers and calipers (even unmatched sets from the same maker) has a strong effect on the kind of braking effects people are reporting. Other things that affect the hardness of the brakes' feel are the degree of toe-in at the pads, the amount of looseness in assembly--some looseness is necessary so they move at all--and the tendency of cable sheaths to squirm as longitudinal force is placed on them. (After all, there IS a reason why gear cable sheath is different!) Of course, it is possible that some calipers are so flimsy they're actually noticeably flexible (e.g., modern department-store bikes).
Furthermore, there are at least minor differences in the frictional coefficients and hardness of pad materials, especially if you include things like sintered metal pads in the evaluation. Of course, rims are part of the system too, and rim materials have an effect. Chromed-steel rims, for example, make most brakes "grabby" when dry and ineffective when wet.
Steve Maas
Long Beach, CA