I am not sure myself but that is the only thing that makes sense to me. GOOG has corporate customers that have built technology licensed from GOOG into the search/advertising infrastructure of their web platforms (advertising in this case might include presentation of links to additional products Target offers based on the keywords and context supplied).
Think about it. If you were Target, do you think your IT/web team can out code GOOG? Those companies faced a classic "buy vs. build" decision and opted to buy from GOOG. They are merchandisers, not web search experts when it comes to core corporate competencies.
If I could afford to buy all of them, I would not need to buy any of them and I sure wouldn't be spending time on the message boards!