[Wiisass]

If a company makes a brake kit for your car then they will list it as a brake kit for your car. There could be a chance a random caliper would mount to your spindle or upright, but even if it does, it's going to be a lot more work trying to get everything you need. Rotors have different offsets, the center of the caliper will be different depending on how it mounts, etc.

Size of the wheels is a factor. If you can't fit the caliper under the wheel then obviously that kit is not for you. Offset and spoke design is another thing that needs to be considered. Bigger calipers may not fit under some wheels due to the way the spokes are designed. That's why many wheel companies offer different faces for their wheels so that they can make sure that the wheels will fit bigger brakes.