Walling says these changes are intended to "get new players into the game faster." They're also a response to a low number of people in those level ranges. 1 - 20 and 70 - 80 are unchanged, but experience gains in the mentoring system are getting a boost to encourage higher level players to help new folks and alts level up. The benefits scale based on level, but players who are mentoring will gain between 50% and 300% extra XP from combat.
This is an answer to a big problem in these types of games; they become top-heavy, and an insurmountable barrier to entry goes up. At this point, though, does it even make sense for it to take 100 hours to reach 70? Why not just 50? If it's not fun for 164 hours, it's probably not for 100 either, right?