Companys pay you more money to review their product or advertise depending on the amount of rss subscribers you have. Would a company like microsoft want to pay a blog with 10 readers $1,000 to write a review on vista, or pay a blog with 100,000 readers $1,000 to write a review on vista? Obviously the one with the most subscribers. Then their product will get a bigger audiance and more people reading about it.
The 24 ways to increase your RSS subscribers is at the link below...
This is extremley helpful to loads of people who have blogs and websites. Let me know if i can add anything to the list, and if my post is good.