As day tripper points out, you should be asking two other questions:
- How many pounds (properly dried) per plant?
- How many plants per acre?
Depending upon the variety, the 0.5 to 2 lb is accurate. The lower numbers will come from trying to grow noble varieties on US soil or some of the other delicate hops. 2 lb is a cascade or other hearty variety under ideal conditions. Of course this all assumes you have a very tight control on nutrients, water, pests, weeds and you don't have a drought year. But that's farming.
How many per acre? You can pack as many as you want, but more than 2,000 becomes nearly impossible for anything to get enough light. Outside of the arid conditions of the PNW and CO, we have found 1,000 to 1,200 is more realistic for an acre. We need to provide more room for airflow to get rid of the morning fog that brings molds/mildews with it. We also need more sunlight to drive that moisture away. The number per acre really depends on what your trellis structure looks like and what it can support.
Carrying it to the next logical question, what can you get per pound...assuming you are going to grow commercial. That depends on the region of the country you are in and the final form/quality of the product you are producing. In general, local growers can get a premium for their product but if the quality is low, the brewers won't come back. If it is wet, the brewers will never ask for more than what they can use in a single batch. If they are dried, but whole cone, some brewers won't touch it. That is a very regional thing from what I've seen.