I believe that the FDA permits up to a 20% discrepancy between actual and reported nutrition information. Whether companies are fudging data on purpose to make their food more attractive is anybody's guess.
Just make sure your serving sizes are equivalent when making the comparisons, and you can also Google the item's calories; there are a ton of calorie counting sites out there and you can probably get an idea of what is the most generally accepted nutritional value.
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days