While most companies use their patents to extract licensing fees from their competitors, Apple has made it clear they have no intention of allowing other companies access to theirs.
Clearly that has led to a shift in strategy from Samsung. According to Korea's Yonhap News Service, Shin Jong-kyun, president of Samsung's mobile division, told reporters his company took great pains to ensure the Galaxy Nexus doesn't infringe on any Apple patents.
If Samsung is correct about the Galaxy Nexus being safe from Apple lawsuits, it would make sense for them to phase out the Galaxy S II before Apple's lawsuits can do any serious damage to Samsung phone sales.
As the first device to run Android 4.0 (Ice Cream Sandwich), the Galaxy Nexus is already the logical choice to compete head to head with the iPhone 4S.