It is the force exerted within the glass when it hits the floor that breaks it. If the glass falls on a hard floor like concrete then the force is very big. Effectively the bit of the glass that hits the floor stops instantly but the rest of the glass following behind is still moving. The force within the glass is bigger than the tensile strength of the material and so it fails. If the glass falls on a carpet then the glass slows down over a few millimeters by squashing the carpet. This massively reduces the forces within the glass and gives it a fighting chance of staying in one piece. When a vase hits the carpet, the energy is absorbed and dispersed into the carpet. However, if the vase drops to the concrete, all the energy is concentrated on the point of impact with dispersion causing the force to react and go back into the vase causing a break factor greater than the vase can withstand. This is caused due to the inertia of motion of the particles of the vessel.