Differences in Alcohol Percentage
 

My wife got me a 1 litre bottle of Laphroaig from duty free in Germany and it is at 40%.

At stores here in Boston, Laphroaig is sold at 43%.

Is a special 40% made to satisfy some EU restriction or is a 40% special for duty free in general?

Hi. Scotch whisky by law must be at least 40% ABV, so that is what the general bottlings are. Other countries request the same spirit to be higher say 43% ABV so it will be bottled at that for the specific markets.

Cask strength and higher ABV bottlings would be sold at the same level across the board.

Differences in Alcohol Percentage
 

The 40% ABV bottlings came about as a result of World War II. Since whisky production was halted during the war, the 40% ABV was a concept to increase the number of bottles per cask as opposed to the standard 43% ABV at that time. The 40% has stayed around and over time, through criticism, many distilleries are increasing their ABV to 43% and higher.