Benuser, it's all in the way the knife comes off the counter and is dependent upon chance, gravity and Newton's First Law of Motion ("A body in motion remains in motion until an external force changes that motion"). Everything is dependent on how the knife is both laterally moving as it leaves support, upon the shifting center of gravity and upon any other external forces. There is no reason to assume that the spine or the edge, or the tip or the handle, will be the point of contact with the floor. It's all chance which part of the knife will hit the floor first.
In the case of Kokopuffs' knife falling off his countertop (assuming that Kokopuffs' countertop has an abrupt 90 degree edge), the knife doesn't simply come off the counter and drop down flat onto the floor. Instead, as the knife moves over the edge of the countertop, the knife remains flat along the countertop until the center of gravity of the knife passes over the edge. At that position, the edge acts as a fulcrum point and the knife tips over, off the countertop, with the knife developing a spin. How the spin works out is based upon whether the knife was horizontally spinning when it was on the countertop, the speed the knife was at when it went over the edge and the movable position of the center of gravity of the knife had as it left the countertop. All of that is completely based on chance.
In the case of Kokopuffs' knife falling out of his hand directly onto the floor (Kokopuffs, take this as my making a teaching moment - I will personally give you the benefit of the doubt about your ability to hold onto the knife, but I simply want to make a point about the physics of the situation), as the knife slides out of Kokopuffs' hand, it is supported by the furthermost of Kokopuffs' fingers along the handle, until the center of gravity forces extends forward of that part of the knife supported by Kokopuffs' fingers. At that point, the furthest forward finger acts as a fulcrum, and the knife develops a spin.
In short, it's more than likely that the knife will develop a spin. What is strictly chance is whether the spin results in the edge impacting the floor. What is also chance is what angle the knife will be at when it impacts the floor.
This is all from my high school physics class, which is now closing on half a century ago, so please bear with me if I've screwed something up. Also, this is mostly off the top of my head, so as to reply as quickly as possible.
Worst case scenario is for the knife edge to be the point of impact, for the knife to impact the floor with the plane of the blade at something other than 90 degrees and for the spin of the knife to be towards rotating the edge towards the floor just before the point of impact.
This forum is celebrated for its advocacy of knives with harder steels. That hardness comes often with the flip side that the harder steels are more prone to brittleness. Side pressures along the edges of such knives have often been blamed for knife chips along the edges.
Kokopuffs has a legitimate concern.