It's all about statistics--and 30 is the life expectancy (average), not the oldest they can live. For instance, a bird, the robin, can live to around 15 years old before it dies of "natural causes", but it's life expectancy is about 1 year because so many things kill it (accidents, predator, etc.). There are lots of things that kill living beings besides old age, like lab experiments. So all of these factors work together so that there's a probability distribution and expectation on a being's length of life, even if they're "immortal".
If you use the summary's numbers, a 1/10000 chance of dying on any given day, then that means you have a 9999/10000 chance of surviving any day. You can run that fraction through any number of years to see what your probability of surviving that long is. (9999/10000)^(365*19) ~ 0.5, so you have a 50% chance of making it 19 years. (9999/10000)^(365*30) ~ 0.33, so you have about a 1/3 chance of making it past 30 years old. 1/10000 is slightly too high a death rate to support a life expectancy of 30 years (you can see it's about 19 years since the rate stays the same over time). You can actually back out the exact rate of death if you want to get an expectation of 30 years and assume a uniform daily death rate: x^(365*30) = 0.5 ==> x ~ 0.00006329 (which they probably rounded to 0.0001, or 1/10000).
This is why, even for humans, immortality wouldn't mean that we avoid death. I've read previously that our life expectancy would still be in the 600s, given the current rate of death. If you truly were immortal, I'm guessing that you would take less risks and could drive that number up into the 1000s, but I doubt it would ever get to the 10,000s. The way the world currently is, something is bound to eventually take each one of us out.