But Solaris is not, and never will be, Linux. It's not an open source program. It wasn't built that way, and it isn't licensed that way.
At the heart of the open source model is not the initial price of the operating system, but the rules under which it is used, and thus the process by which it is updated.
Solaris plays by the old rules. Not that there's anything wrong with that. Many enterprises like the old rules of proprietary software. They like knowing there is a "someone" to take responsibility for fixes. They like knowing that there are licensed applications around. And they like the idea that some crazy hacker isn't taking apart the same thing they own, trying to use its features against them.
But free isn't open source. While the differences may be minor, as the French say, "viva le difference!"