Jakob's Law of the Internet User Experience: users spend most of their time on other websites. In visiting all these other sites, people become accustomed to the prevailing design standards and conventions. Thus, when users arrive at your site, they assume it will work the same way as other sites.
[edited by: lorax at 1:26 pm (utc) on Sep. 9, 2007]
To answer the original question, no. Not all shoppers know the top logo is a home link.
I have been an online shopper since the days when you bought things from posters on USENET and eBay probably wasn't created yet. And, I don't think I've ever clicked, or even thought to click, the logo to get to the home page. How intuitive is that?
I wasn't aware of this until a couple months ago when a friend suggested I make my logo the link to the home page, which I still haven't done.
So, don't assume that this is something "everyone knows!" I don't care what Yahoo was doing in 1995; all I remember is that if you click one of Google's decorated logos, it takes you to a page about the holiday.