Estoppel is meant as a protection against the following situation. Sun tells Google, "Don't worry. Android doesn't infringe on our intellectual property." Google then relies on that information when making future plans for its operating system. Sun then comes back and says, "we're suing you for infringing on our intellectual property." Sun (now Oracle) would be reasonably estopped from collecting damages because they had earlier made assertions that Google reasonably relied upon in their decisions.*
Google's lawyers note that Sun offered to license Java to Google (http://www.networkworld.com/news/2011/072211-google-sun-offe...). Therefore, there is no reasonable way that Google could try to claim estoppel. Google was aware that Sun believed that Google needed a license. Therefore, there is no possibility that Google believed that Sun was saying that Google's Java implementation didn't infringe on Sun's IP.
There's a distinct difference between that scenario and the one that occurred. In the hypothetical, Sun has stated a fact "your implementation of Java doesn't infringe". Later, Sun changes that fact "your implementation of Java does infringe". With what Sun's CEO has said, one can create a dialogue that doesn't contradict itself. "We're happy you're using Java"; "We're still happy you're using Java, but you have to pay for its usage or code around our patents like we said before when we offered you a license for Java."
*Estoppel is meant to make sure that people can't trick you into situations (and often times requires some proof that the person being estopped had that motive). For example, let's say that Sun had gotten together in a board room and started saying, "we'll tell people that there are no patents on Java and they can all use it for no charge and then later, once they've all started using it due to our assurance that there are no patents on it, we'll change our mind and sue them for patent infringement." That isn't the case here.
Google's lawyers note that Sun offered to license Java to Google (http://www.networkworld.com/news/2011/072211-google-sun-offe...). Therefore, there is no reasonable way that Google could try to claim estoppel. Google was aware that Sun believed that Google needed a license. Therefore, there is no possibility that Google believed that Sun was saying that Google's Java implementation didn't infringe on Sun's IP.
There's a distinct difference between that scenario and the one that occurred. In the hypothetical, Sun has stated a fact "your implementation of Java doesn't infringe". Later, Sun changes that fact "your implementation of Java does infringe". With what Sun's CEO has said, one can create a dialogue that doesn't contradict itself. "We're happy you're using Java"; "We're still happy you're using Java, but you have to pay for its usage or code around our patents like we said before when we offered you a license for Java."
*Estoppel is meant to make sure that people can't trick you into situations (and often times requires some proof that the person being estopped had that motive). For example, let's say that Sun had gotten together in a board room and started saying, "we'll tell people that there are no patents on Java and they can all use it for no charge and then later, once they've all started using it due to our assurance that there are no patents on it, we'll change our mind and sue them for patent infringement." That isn't the case here.