Advertising icons are hard things to pin down.
I mean, it should be easy, right? For a brand icon to be considered iconic, it should in some way visually represent the name of the company as a whole - the Chili's logo is a luscious red chili pepper; the IBM logo, while not that inventive-seeming nowadays, does have the advantage of telling you exactly what company it represents (though, admittedly, not what it does).
But what do you do with a company whose logo holds no iconic representation of the company at all? By the common rationale, the word "Swoosh" would mean nothing to you, and yet it's practically a given that reading that word made the name "Nike" spring into your head. The Nike Swoosh is, in reality, one of the earliest and most successful non-representative corporate icons in history.
What Nike did was open up a whole new world of brand perception, the kind of thing that makes market analysts start to uncontrollably salivate; the determination of a corporate logo's iconic perception, a thing that used to be as easy to determine as looking at a brand logo and seeing what comes to mind, is now a far more complicated issue for the typical ass-backwards reason.
In a nutshell, truly representative company logos are sometimes as hard to pin down as their more ambiguous counterparts - if I showed the average person four iconic representations of, say, a Puma, and asked them to tell me which one was the logo for the Puma athletic company, many of them would be hard-pressed to tell me which one fit. If, however, I showed the same person four different versions of another brand with a totally non-representative logo (say, Chrysler) the same person would be right a huge portion of the time because the brand's presence is that powerful.
This stuff is vitally important for a company to know. It's studies like this, for instance, that told Mars that the Snickers brand was recognizable enough to create print ads that feature fake words (like 'Nougatocity") written in the style of the real Snickers logo - it's the study that told them that people weren't going to look at the ads and thought "what the hell is that," or worse, "Oh! Milky Way!" It's also these kinds of studies that tell companies what other icons the people who recognize your brand also tend to recognize so you know where to spend your advertising money.