The actual ruling document  should be quite readable by most participants here; I recommend a look. It actually reads more like tech speak then legelase, and appears to do a thorough job of laying the foundation for the decision. It indeed goes back to the history and Sun's intentions before the Oracle purchase.

The really good news goes beyond the specifics of the case, as most Supreme Court rulings do. It provides a conclusive ruling, unlikely to be challenged again in our lifetimes, that APIs as a category of software cannot be protected as intellectual property. While Google was acknowledged to have copied Sun/Oracle's API code, such copying was confirmed to fall under "fair use" exceptions to copyright infringement. Different variations of fair use allow for legal (ie, "infringing" but exempt from action)  copying of works for the purpose of satire, education, home backups etc.

(This case, before the ruling, took up one of the weekly lecture sessions of the Harvard CopyrightX course I am currently taking. In a straw poll of the class a few weeks ago I was one of the few who argued that and why Google should prevail. Much of the rest of the class sided with Oracle. The next session will be fun.)