Sun's interest is in breaking the M$ near-monopoly on office suites and corporate PC operating systems. Sun's core business is hardware, not office suites. But if customers have a bigger choice of OS, and can use Star Office on a Solaris or Linux box, Sun can sell more hardware.

And there are two versions because that is what the market requires. Open Office because it is a free download, you can't compete without that, and Star Office because many corporate customers have an aversion to free, open source software. They want to pay someone for everything, so they have a throat to choke when it breaks...