Valid point.... HOWEVER, let's look at the fine print.
Let's take Halls Performance Racing's location into consideration when we make note of the added 3 horsepower that the Snipers made. Hall's is located in Glendale, Arizona.
On March 16, 2011, the average temperature of the day was 70.2 degrees Fahrenheit, with a barometric reading of 29.92 IN.
On May 27, 2011, the average temperature of the day was 85.0 degrees Farenheit, with a barometric reading of 29.72 IN.
Without knowing the exact time of day these dyno runs were made, we have to take into consideration the average for the day. I'm sure an ambient temperature difference of ~15 degrees would play a part in an increase in power, no? Without knowing humidity levels, this is the best assumption I can gather.
Source: http://www.almanac.com/weather/history/zipcode/85301/2011-03-16
Source: http://www.almanac.com/weather/history/zipcode/85301/2011-05-27