The rules treat Relief Areas as penalty free OB areas, so all of the rules for OB also apply to Relief Areas
Casual Areas are different from OB in a couple ways and this leads to some of the differences with regards to lost discs.
- OB areas may prohibit a player from entering that area, so locating a disc may not even be allowed. Players can play from Casual Areas and so players can freely enter the area to find their disc.
- The next lie for discs in an OB area is based on where the disc entered the area, so location of final resting place is not required to determine the lie. For Casual Areas, the next lie is based on the position of the disc which requires locating it.
And yes, we've had questions from players that wanted to extend the old muddy puddle Q&A to evergreen trees, thick layers of leaves in the fall, snow and more. There needs to be a line someplace, and where we have it (exception for OB/Relief Areas only) makes it the easiest place to draw that line.