Having owned both VW Passat and Lexus, I can say that the Lexus leather is extremely soft and therefore does require some care compared to VW leather which is harder.
What you've pictured is not uncommon on the IS and thats because the seats have decent side bolstering. If you get the car from Lexus, insist that this is taken care of beforehand, it'll prob only cost like £100 if you get it done but they'll be able to do it. To be honest, most cars with decent seats and soft leather will result in this - look at any Audis with super sports seats with the nappa leather, it practically rubs off in that region.
Having said that, its MORE common on LOW MILEAGE cars. This is because low mileage cars usually get driven in town and therefore previous owners have been in and out more than on a higher mileage vehicle in most cases.