I want to serve visitors originating from search engine queries different options such as "see more widgets like this one", but due to space constraints and different user objectives, leave that off IF the visitor got to that page via another method, such as browsing from the home page and ending up there via normal search (in which case the visitor knows there are other widgets like that one).
When cloaking (this does fit the strict definition of HTTP_REFERER cloaking) there is always risk. But I suspect it would pass the test in a manual review. Also, it could depend on exactly what you are displaying to the viewer.
I have the feeling that they are more likely to penalize those pages that remove something when human visitors show up, because that would be equivelant to hidden text or links.