I think I can clarify a little what HappyEnding means. Basically, you take into account the cost of each item, but not the value and thus the associated true cost. For instance, as you buy more resistances you get diminishing returns for the value of each point you buy. Your first 100 points of magic resist will yield a 50% reduction in damage, but your next 100 points will only yield an additional 25%, bringing you up to 66.7% reduction. This means that while the cost may stay constant, the value of each stat may change as the game situation changes. For instance, as olaf you may not want to buy nearly as many resistances as you would with maoki because his ultimate gives him resistances when activated, reducing the value of any points of resistance bought.
However I don't think the same rule applies with health, because at 1,000 health your next 1,000 health purchased will give you the same increase in effective health.
Here is a sample (totally inaccurate but w/e)
Maoki with 100 armor and 1000 health vs maoki with 200 armor and 1000 health vs maoki with 2000 health and 100 armor
1st maoki - 2,000 effective health vs physical
2nd maoki - 3,000 effective health vs physical
3rd maoki - 4,000 effective health vs physical