I'm sure he's making money on the portal thing as long as he monitors traffic accurately.
Example: you know exactly what each domain cost you, your renewal costs are very low (I expect he gets names at close to $6/yr), you know what each site visitor generates in profit (on average, after deducting overheads such as bandwidth), and you have a pretty good idea of how traffic drops off on domains over time. From that you can determine a break-even point where you know that if a domain generates X visitors/sales in the first 3 months then the domain is worth renewing (otherwise you let it drop). With a bit of programming skill this could all be automated so the break-even is updated over time and renewal decisions are made automatically.
Moral if the story is don't grab just for traffic anything he lets drop.