I agree that once you reach level 37 (well, for most people anyways) it is kind of depressing thinking "well, this is it... my build is complete and I've reached the end." However if 38 gave you attribute/skill points the same as every other level up does, and it was much easier to reach, then the average level would go up even more, and to be honest having the game-breaking average level of 36-37 is already way too high. If they made it so you stopped getting useful things at level 37, and each level afterwards was simply to enable you to get a better title upon retirement, or maybe a title without even retiring, or maybe an instant loompoint, etc., then I see no reason not to lower the xp required for subsequent levels.
And yes HESKEY, they toyed with the values of the hall of fame to accommodate the new leveling system. Took me a while to understand what happened first time I looked at it as well. Really, Kinngrimm just retired at 36.45 and they added 3 levels to it. I would bet that, despite the fact this community has a large number of sperglords, no single player has gained enough xp in their entire crpg career to have reached level 39 by now, even if they never retired. 5 BILLION is an insane amount of xp to grind... aldogalus was the highest leveled player in all of NA, maybe the entire mod... he was 37 pre-patch of destiny. The old level 37 was at 1 billion or so xp. Aldo never retired (as far as I know) and he played very often (I personally saw him almost every time I played), for roughly 4 years straight. All that time, only to get to 1 billion. To put things into perspective, it would take him another 16 years to get to level 39 in the new xp system.