Why does ethanol have a health rating of [2] in NFPA 704 whereas methanol, which is far more toxic, has a rating of only [1]?
I believe that the rating is dependent on toxicity tests. 

The acute oral toxicity LD50 value of acetone is 5800 mg/kg

The acute oral toxicity LD50 value of methanol is 5628 mg/kg

The acute oral toxicity LD50 value of ethanol is 3450 mg/kg

Low LD50 values means that only a small amount of chemical is needed to kill someone. According to these values, you would need to ingest a larger amount of acetone or methanol to die.I am not sure how valid these toxicology test are. Fun fact: fructose is deadlier than methanol according to LD50 values.

Furthermore, there appears to be some variation in the values as well. Wikipedia lists the LD50 value of ethanol as 7,060 mg/kg. 
Maybe this question can be addressed at Biology SE.