When you're selling software by direct mail or at your Web site, you've got to give prospects a LOT of detailed product information. Because if they're going to part with their money, they're going to want to know all the benefits, all the specs, all the nitty-gritties. When you're asking for the sale, you simply have to answer readers' questions and overwhelm them with compelling reasons to buy.
Lead generation is a completely different animal.
The object of your direct mail, e-mail, ad, whatever, is NOT to make the sale immediately, but merely to get prospects to raise their hands and identify themselves. Once they make themselves known, they enter the sales cycle and you can convert them into paying customers down the road. There are many. For example, when you're doing lead generation, the selection of your free offer becomes crucial. You have to pay a great deal of attention to developing a killer offer that maximizes response.