(A post from Halcyon on eqclassic that explains it well)
Hell levels were just the result of the formula used to calculate how much experience you needed to level. If you look at the formula you can see why those specific levels take that much longer.
http://www.webslinky.com/darkomen/xp/eqexp3.html
Also, looking at the formula, I would make an educated guess and say that they did not intend for the hell levels to be there, but rather for sets of levels to take longer. i.e.: The experience required to level from 35-39 should increase at a faster rate (or accelerate quicker for people that understand that) than the the experience required to go from 30-34. A side effect from that paradigm is that the first level in the new "block" will take that much longer.
As for being built into the client, I 'm guessing it was to save time on calculations or they used it as reference or something like that. Since there is a formula for levels and it differs based on race and class I can't see any other purpose for it to hard coded in the client. I doubt it was in there as "hell level, this should take longer" or anything like that.
This easier formula should explain it better. Say the forumla for the experience required to be a level (L) is as follows:
expNeeded = L * x
From levels 1 - 4, x = 1 and from levels 5 - 9, x = 2.
The amount of exp you need to be the level L is then as follows:
Code:
Level Total Exp Exp needed to
Required complete level
-----------------------------------------------------------------
1 1 1
2 2 1
3 3 1
4 4 1
5 10 6 <--- Hell Level
6 12 2
7 14 2
8 16 2
9 18 2
Regards,
Mg