If I look up top round steak, it has about 65 g of protein in an 8 oz serving. If it takes roughly 3 lbs of top round to create 1 lb of jerky, I would expect the jerky to contain about 24 g of protein per oz, but it looks like the average is closer to 10 g per oz in commercial jerky. Is this because they aren't using top round steak or because some protein is lost in the process? If I make my own jerky, will I expect the same amount of protein in the finished product as what I started with?
Yes, it's mainly because they use different muscles. For example here's jerky that contains 21 gram of protein Fatman beef Jerky.
During dehydration you don't remove any calories so you cannot have lower amount of protein, fats or carbs. You just remove water.
What is more important when looking at jerky is that little extra text in nutrition box. As you can see in Fatman there is info about Calcium and Iron.
In other jerky where proteins are around 28% You can see they added a lot of "extras" "Healthy jerky"
So they used what's called "lean beef". A beef that contains 14 grams of protein peer 100g. It's a beef that is usually very hard on it's own and that need a lot of beating (or marinate) to make it chewable.
If you want to make jerky at home I suggest entrecote. It's a little bit more work (due to fat) but it's around 26g of protein and 15 grams of fat per 100g.