d20 Encounter Calculator - Discrepancy

[zelduck]

http://www.d20srd.org/encounterCalculator.htm

Difficulty8:......% of total9

Very Easy:.......0%
Easy:.............10%
Challenging:.....50%
Very Difficult:..15%
Overpowering:.5%
Unbeatable:....0%

Either I'm missing something, or the percentages only add up to 80%.
I don't have my DMGv3.5 on me right now, but I think that this is a problem in the book, not the calculator.
Still, since I don't have it on me, I'm not sure, so I thought I should let you know.

Also, if it IS the book's problem, anyone know if there's been any errata released for it?
Or, if there's no errata, anyone have a homebrew solution?

I was thinking something along the lines of
E: 15
C: 50
VD: 25
O: 10

Edit--OR if you want to stay closer to the original proportions, this might make more sense
E: 15
C: 60
VD: 20
O: 5

[zelduck]

I just checked my DMG. The missing 20% goes to a situational encounters category.
I.e. 1/5 of a good campaign's encounters should involve some interesting dynamic that, if handled properly, shouldn't be too hard for the PCs, but could potentially be dangerous.

Very Easy:......................0%
Easy:...........................10%
Easy if handled properly:...20%
Challenging:..................50%
Very Difficult:................15%
Overpowering:.................5%
Unbeatable:....................0%