Here are a couple of reference for the background on the topic http://www.theguardian.com/sport/blog/2010/apr/13/the-question-why-is-offside-law-genius and the book ''Inverting the Pyramid'' Chapter 19.
They both talk about the 2005 FIFA amendment to the ofsside rule contributing to stretching the game.
Specifically they imply the following.
- The amendment means the offside player must touch the ball of block a defender for the referee to call the offside foul.
- This discourages the team from playing high offside line and "stretches the playing area from 35-40m to 55-60m"(from the book) and avoids "goal hanging" "without the side-effect of legitimising the offside trap"(from the link)
I don't get that second bullet. Yes the foul is not called until the attacker goes and touched the ball, but how is that going to stop the defenders from applying the offside trap? A team would still play a high defensive line and make sure the target of the long pass is offside. All that changes now is that a foul is not called, but the attacker is still out of the play because he was offside. So why would any team be discouraged from using the offside trap?