I think the reason this happens is because there is a belief that, and who knows maybe it's the truth, people buy emotionally. Business and marketing books (E-myth and How to win friends come to mind specifically) constantly parrot that "sales studies" and "marketing research" show that people buy, or this case download, with their feelings. This seems to lead people to add vacuous fluff to marketing pages to "appeal" to someone's emotions.
As you can tell by most of comment I think this isn't the whole truth and that really things live somewhere in the middle and that the domain and scope of interaction greatly shift this spectrum one way or another, picking a doctor/lawyer vs picking and IDE comes to mind for myself, YMMV with that example and might even further drive home the point.
Long story long, marketing is hard and the people doing the marketing often aren't domain experts and have to rely on the information passed to them through a convoluted game of telephone via authors and experts that can't even communicate everything needed to be effective because they themselves aren't good at teaching.
As you can tell by most of comment I think this isn't the whole truth and that really things live somewhere in the middle and that the domain and scope of interaction greatly shift this spectrum one way or another, picking a doctor/lawyer vs picking and IDE comes to mind for myself, YMMV with that example and might even further drive home the point.
Long story long, marketing is hard and the people doing the marketing often aren't domain experts and have to rely on the information passed to them through a convoluted game of telephone via authors and experts that can't even communicate everything needed to be effective because they themselves aren't good at teaching.