It’s a well known problem. But plenty of other cars have issues as well. Ford’s 3.8L has an even worse head gasket problem in addition to problems with the aluminun valve bodies in the transmissions used in the Taurus/Sable and Windstar. Dodge has tranmission problems with their “Ultradrive” transmsission in the late 80’s and early 90’s. The 3.1/3.4L GM V6 had a well know intake gasket problem. Toyota and VW had problems with sludge build up in their engines a few years ago.
The point is no automaker makes a perfect car, even the ones with a repuation for great reliability. Subaru stepped up the plate and offered to cover repairs for 8 years or 100k. That’s a better offer than most other automakers offer.
I can’t help but notice, that the turbo models (WRX, Forrester XT) don’t seem to be affected. I guess that’s because the used lower-compression pistons/heads on those. Strange that a tubrocharged car would end up having fewer problems that it’s N/A counterparts.