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.
I know this is old but I thought I'd add my experience. I would question that dehydration mass change. I just made some jerky and the weight was only halved, not reduced to a third.
That would partly explain the discrepancy in your expected protein content of commercial jerky. My jerky was quite dry like old leather but if you reduced it by two-thirds it would be more like crispy crackling. The jerky that I've bought in stores I would estimate is the same dehydration level as the batch I just made, so only reduced by half in mass.
The other variable would be the cut of meat used. I used Silverside and it had 20.5g of protein per 100g, compared to your top round example which works out as a quite high 28.76g per 100g. I would guess that commercial jerky probably uses a lower protein content cut than that. And that would explain most of the difference.
So for my jerky, made with Silverside, you would get a protein amount of 11.6g per oz. Very close to the 10g per oz for commercial jerky you quoted.
TLDR: no the total protein amount should not change with dehydration.