Level cap is arbitrary. It could be 60 or it could be 500. When it's 60, as Bash, claims it works well with increasing your power each time you level. If it were 500 you'd get levels every few minutes and be getting minuscule improvements each time -- this would be ultra lame. 99 doesn't work for D3 so we get 60... that's completely fine with me and to be honest the WoW comparisons here are really misplaced. Next people will be like "ZOMG I saw the color red in Diablo, but they used the color red in WoW too! WTF Blizzard stop cloning WoW!"
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