There is another factor involved, and if you look carefully at the wording of the two quotations and the dates, I think you will see another reason.
In the early decades of sport diving (I am choosing my terms carefully), the US Navy tables ruled diving. If you wanted a 2-tank dive, you had to wait out a surface interval. The US Navy surface interval was determined by the off-gassing of the 120 minute theoretical tissue (compartment). This worked fine for the US Navy, but it was not so fine for the sport diving industry. Navy divers usually did only one dive per day, so they didn't really care what the surface interval was. Sport divers wanted to do more than one dive, though, and the Navy surface interval was extremely long, resulting in long waits that made dive schedules a real problem.
In the early 1980s, PADI research on sport diving showed that the 120 minute compartment was unnecessary for that kind of diving. For most dives the 40 minute compartment would work, but they went with the 60 minute compartment when they made their new tables. They also shortened the first dive limits and made more pressure groups to decrease the amount of rounding necessary. Finally, they eliminated decompression diving from the tables, end the dives at the point that a decompression stop would have been needed. This resulted in a dive table aimed at sport divers, people doing several shallower, shorter dives per day than the Navy did. They could now complete those dives in a reasonable amount of time without waiting interminably on a boat for the time they could start the next dive.
In order to differentiate the new tables from the old ones, they gave it a new name--the Recreational Dive Planner. Divers using that planing device had to stay within its limits, because if they violated them, the tables could not be used again until sufficient time to wash out the nitrogen and start over again.
That was about 1984--after your first quote and before your second.
