i think he means by selling links is a good way to go if you have a high pr site...
for example text-link-ads will give you $5 per link per month if you have a site with PR4 and about $50 per link per month if you have a pr6 or PR7 site...

so that means if you have a PR4 page, and you put 8 links in it for $5 per link, you are guaranteed $40 a month and if you have like 10 pages that has PR4... just multiply that by 10... $400/month
I hope that helps