This is fairly simply explained:
* There is one unit of measurement, SAR
* There are two maximum permissible values; one for the US, one for the EU
* Apple has chosen the higher of the two so they can make a better phone (more power)
* They get away with going over the US legal limit by recommending you hold it further away than normal<p>It should be noted that not only are the max SAR values different for the EU and US but they are measured differently so can't really be compared directly.