The 2008 generation change is best explained in the context of the Society's previous positions on the "generation" of Luke 21.
In Luke 21:32, Jesus said that 'this generation will not pass away until all these things occur.' For decades, the WTS taught that Jesus was referring to the generation of people who saw the events of 1914. The WTS taught that there would be some people from that generation alive when the end came.
Well, in 1995, the end still had not come, so the WTS changed its teaching on "generation." They now taught that Jesus just meant "wicked people" when he said "generation." And, most importantly, generation was no longer tied to 1914. In other words, everybody who was alive in 1914 could be dead before the end comes.
In April 2008, the WTS tweaked its generation teaching once more. But this "new light" was not nearly as significant as the 1995 change. In 2008, the WTS said that "generation" as used by Jesus in Luke 21 didn't really mean "wicked people"--rather he meant "anointed Christians." But it is important to note that this did not change the 1995 understanding regarding 1914. In other words, the party line is still that everybody alive in 1914 could die before the end comes.
Of course, the Society still teaches the end is right around the corner. But there is no temporal boundary--no date or other marker by which the end must come.