Hi,
So since it's winter I one morning discovered that my IS200 had the same problem. The back heats up just fine but the bottom part doesen't. I took your advice and checked the fuses. I found a fuse on the drivers side (left side of the car in my case) that was named SEAT HTR. Now i'm thinking this is the heated seat fuse, but is there really one fuse for two seats? Anyway that fuse was ok so i'm out of ideas. Don't really want to go to the dealer as well with this minor problem.
P.S I recently had my sound system upgraded, and i wonder if those quys maybe messed it up.