In 2000-01, Pavel Bure scored 59 goals.
The top 5 goal scorers that year were:
Bure, 59 goals
Sakic, 54 goals
Jagr, 52 goals
Bondra, 45 goals
Kovalev, 44 goals
In 81-82, Gretzky had his NHL-record 92 goal season.
That year, the NHL goal leaders were:
Gretzky, 92
Bossy, 64
Maruk, 60
Ciccarelli, 55
Vaive, 54
As you can probably see, it was easier to score goals in 81-82 than 2000-01. Therefore, one can argue that each of Bure's goals was more difficult to score, and thus "worth" more.
Ultimately, when adjusting those goals, Gretzky gets 68 adjusted goals, because it was relatively very easy to score goals in the 81-82 season. Bure gets 65 for 00-01 because it was a relatively difficult time to score goals.
So the way it comes out, Gretzky's season was "worth" 68 goals, and Bure's was "worth" 65. It's an estimation of the goal value relative to the era.