Bryan Catrill says one thing.
Danese Cooper who was responsible for drafting the actual license while at Sun says another thing.
Obvious business sense stands firmly with Danese, it would be very stupid of Sun to hand over the best technological advantages of Solaris to their main competitor, which was Linux, while struggling against it in the market.
Open-sourcing Solaris was a last ditch effort from Sun to attract mindshare (and eventually market share) back from Linux, that plan would be doomed beforehand if Linux could just pick the best parts of Solaris for inclusion.
Sun NEVER intended for Linux not to adopt it. They wanted it to be ubiquitous across all open source platforms.
IMO they should have two claused FreeBSD licensed it but they didn't.