Keep in mind he is talking about hiring someone for their time and not based on per word or per article. Someone that can write decent 5-8 decent articles per day.
Yes, you can do the calculations on what that person would get paid if they got paid per article (at a somewhat premium price each) - and that's IF they would be able to arrange that same amount of workload without this customer. Keep in mind, it doesn't matter how much your articles are worth if you aren't busy - the free time means that you are leaving money on the table. What the OP is guaranteeing a fixed amount for constant work... so this isn't for people (or organizations) that already get alot of business, this is for someone that can write well and wants a guaranteed income.
Hope this helps...
