The rule change wasn't really necessary.
Basically, the rule change states that when the OB line has a detectable thickness, the disc has to be actually touching in bounds (not just the line), to be considered in bounds.
The best example of why this rule was changes is this...
Your disc comes to rest out of bounds, but leaning on an OB marking fence. Since the fence (OB line) is now considered OB, the disc is also OB. The line used to be considered good, as in tennis.