3D applications have different approaches to processing matters; the way in which their functions handle things are distinguished. The algorithms in which they calculate certain processes are different formulas. In this respect they resemble people all of whom have different talents and different things at which they suck (pardon my French). The image below is an example of the different way of handling of matters.
The fillet of the object at the top is irregular while the bottom one is smooth. It is an angled joint of two pipes of a different diameter - one of the constructions that a number of 3D programs do not handle well. The fillet actually looks like a real life weld of welder who was not too skilled. Also the fillet command disrupted the surface of the slanted pipe. The application producing the poor filleting does an excellent job at other types of modeling, rendering and creating animations, but this particular function gives bad results. It is probably why many 3D artists use various applications to achieve whatever they want to achieve.