[saalweachter]

Anecdotally, my experience has been that while yeast cultures are durable, you can also get some maladaptive selection going from time to time; eg, if you are too irregular in feeding your starter, you might end up with a slow-growing culture rather than the fast-growing culture you get from feeding your starter twice a day and want for a good rise. Your starter will still be alive, but not as useful until you start feeding it constantly again and get that fast-growing culture established again.