They haven't been married for very long, not even a year I think. When people are already that unhappy and don't have a longer, extended "honeymoon" period, the marriage might have been a mistake in the first place. I think Jana is well on her way to what will be her second or third divorce.
Yes, since they are separating, they likely will get divorced, unless they seek counseling and have a change of heart. Although they've been married for over a year, these celebrities have busy lives that keep them apart for long stretches. This makes it hard to work on a relationship. If they're not more committed to their marriage, they'll likely divorce.
People don't take the very large step of separating if they are happy in the relationship. It's clearly the first step before a formal divorce. They've only been married a year, so it's not surprising that they are simply going to call it quits. Marriage isn't all that it's cracked up to be, obviously. This is Kramer's third marriage already.
This story is not a surprising story with any celebrity couple. Yes, they will get divorced especially when they have already separated from one another. This is a common occurrence in the lives of celebrity and is not shocking in the slightest. However, what has become shocking in Hollywood is when celebrity couples last for years and never come to the finality of divorce.