It is an online marketing truism that every hurdle you put between prospects and the purchase confirmation page will increase the purchase drop-off rate. For example, a purchase process that has eight pages will have fewer completions than one that has four pages. I believe it is this "fact" that has driven marketers to inject prospects as far down the purchase funnel as possible, and no longer to merely drive users to the homepage.
It is also true that if a prospect has "raised her hand" by searching for a specific product by name or by clicking on an ad promoting a specific feature, that linking her to that specific product or feature page is more effective for conversion than dropping her off on the homepage and requiring her to again search out the product she is looking for. I believe this is the second major factor decreasing the number of site visitors entering via the homepage.
For brand marketers, whose companies don't or physically can't provide online product fulfillment, the obsession with increased conversion rates is not the end-all be-all. While these marketers want to get their prospects to take certain actions (download a brochure, enter an email, sign up for a product test drive, et cetera), they are measuring the success of their site and their online marketing campaigns in terms of the value of the customer interaction. They are always asking themselves: Did I get the prospect the information she was looking for, and will they tell their friends about my product and service (and site)?
Along with search engines, directly entering the marketer's brand URL is often the jumping-off point for a lot of consumers who are researching a purchase. This is pretty intuitive because URLs are hard to remember. For example, remembering the URL for the fifth sub-page of the third site section to get to the washing machine product details page is harder to remember than PCRichards.com. It is in these early stages of the purchase process -- the research and discovery phase -- that the homepage is critical.
The cliché, "You never get a second chance to make a first impression," was never truer than it is for online marketing. Customers are just one click away from your competition, and they are likely going to hit your homepage in the process. So, although new site access patterns have emerged and will continue to multiply with new channels and devices like mobile and iPhone, a company's homepage is still an important stop on most consumers' road to purchasing.