To make sure they stay in business? I think a lot of people are more than happy to pay for useful services just to keep them in business. As long as the utility is larger than the price charged transactions will be made.
One website I'm familiar with has a freemium product, lots of users there pay just to support the site, even if they never actually use the premium bits.
Ok, why would you pay for Dropbox of you didn't have to and they didn't ask you to? They clearly are not going out of business, at least until something better comes along.
One website I'm familiar with has a freemium product, lots of users there pay just to support the site, even if they never actually use the premium bits.