From what I've seen in two minutes of intense web research, an inflated football weighs roughly 14 to 15 ounces. Here's a more detailed analysis, which estimates the weight of air in a football at a pressure of roughly 13 PSI at 9.67 g. That means that if the footballs are underinflated by 10% above atmospheric (5% absolute), the football weight would be lower by roughly 0.5 grams.
So, if the football weighs something over 400 grams, what is the expected deviation of the football's weight by manufacture, and by environmental change?
Link: NFL Football Weight Calculation
That's not to say that it does seem odd that ALL of the deviations were on the low side. However, the Colts are sore losers, and the Pats won the SB without deflated balls, if just barely.
The question could be relevant IF...
...the officials failed to weigh the Colts' footballs...
'Cause if they DID weigh the Colts' footballs as well, then to have all 12 Colts' footballs in sync -- and almost 90% of the Pats' footballs out of sync...
...that'd be difficult to pin the blame on the manufacturer -- assuming both teams get their balls from the same source. Right?