Here is how I view it. Use of something on the web without attribution in some way = possibly some form of stealing, depending on the "rules" associated with the object. Use of something on the web with attribution in some way (even if the attribution is really very slight, like a link to some site) = not stealing, but might be some sort of breach of conduct of some kind. This is not to say that all use without attribution is stealing as I think how something is use is important too, but no attribution is riskier and ickier in my mind than use with attribution.

Or another way of saying this - If the company had said "We love this logo and we are using it here" I would have not said anything (that is, if they made some effort at attribution). Or if they had used the logo but it had been for a different use, like just as part of their web site or a blog post, then I would not have said anything. But to take someone else's art, and to use it without attribution for one's company logo, that to me had crossed some sort of line.