Regarding Protein in canned vs. dry from http://www.catinfo.org

Another important issue with regard to the protein contained in a dry food is that it has been cooked at very high temperatures for a long period of time. This extensive cooking required to dry the product significantly decreases the biological value of the protein sources.

With regard to the overall protein amounts contained in a food, do not be confused by the listing of the protein percentages in dry food compared to canned food. At first glance, it might appear that the dry food has a higher amount of protein than the canned food—but this is not true on a dry matter basis which is the accurate way to compare the two foods. Most canned foods, when figured on a dry matter basis, have more protein than dry food. And remember, even if this were not the case, the percentage numbers do not tell the whole story. It is the protein’s biological value that is critical.
In the wild, your cat would be eating a high protein, high-moisture content, meat-based diet, with a moderate level of fat and with only approximately 3-5 percent of her diet consisting of carbohydrates. The average dry food contains 35-50 percent carbohydrates. Some of the cheaper dry foods contain even higher levels.

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Cats have a physiological decrease in the ability to utilize carbohydrates due to the lack of specific enzymatic pathways that are present in other mammals, and the lack a salivary enzyme called amylase. Cats have no dietary need for carbohydrates and, more worrisome is the fact that too many carbohydrates can be highly detrimental to their health, as I explain below.
And here is a great table for those interested in the dry matter percentages in many canned foods, already calculated for you. I keep a copy of this in my purse when shopping for canned food.

http://www.geocities.com/jmpeerson/CanFoodNew.html

An Open Letter to Veterinary Professionals

An excerpt

Have you ever seen a barn cat barbecue and dehydrate its mouse dinner and top it off with a dessert of corn gluten meal soufflé? Or heard of a cat that went hunting for rice grains or oatmeal for breakfast? No? It would be illogical to feed an obligate carnivore a steady diet of meat-flavored cereal, right? Then why are we continuing to feed cats like they're herbivores? Hopefully, many of you read the "Timely Topics in Nutrition" article in the December 1st 2002 Journal of the American Veterinary Medical Association (JAVMA) titled "The Carnivore Connection to Nutrition in Cats". After reading this, I wonder why anyone advocates feeding grain-packed commercially prepared dry food to a cat.