I don't think you need to work on side projects to be a great programmer. It's just that there are very few great programmers who don't have a variety of side-projects. It's a natural side-effect of the desire and curiosity that leads people to become great. They don't see side-projects as some sort of drain on their free time.

I don't think it's a bad thing if you don't aspire to "greatness" though. There's plenty of jobs where a decent, reliable programmer is perfectly fine. 49% of us are below average, after all.