I daily drive my Star Specs in warm weather and rotate them every other oil change (~6k). I have just over 13k miles on them now and they're wearing pretty evenly with a fair amount of life left. Last I checked, I believe they've just passed the first of three wear marks, so your ~20k estimate is probably about right (+/- ~10k, depending how hard the car is driven).
Keep in mind that if you were to damage one tire beyond repair (it happens), it doesn't really matter how long the tires last since you'd have to replace all four at the same time. Freak accidents can happen any time... some crap in the road is just unavoidable.
When it comes down to it, I'd rather have good tires with good performance that have to be replaced more often instead of mediocre tires that last forever. Gotta pay to play, so they say.
07 WRX (Albins 5MT + Blouch 20G)
Jorge Carrillo Tuned (365 whp/340 wtq)