It's different because Infiniti (at least in the FX) heats seats through blowing hot air like climate control blows hots air through the vents.
This is also why efficiently our cars can get cold seats in the same way.
This is also why our FXs have filters below the seats since it pulls the air from there I believe to cool/heat the seats.
Most american cars have heat pads....they are independent of the car warming up and hence warm up fast and very very hot....sometimes way to much, but yes fast, but you also don't get cooling seats, which I love in the summers.
Mine are slow to warm up, but after driving with heated seats for 20 minutes, it can get really hot and sometimes need to turn it down. I've had heated seats in a cadillac and it gets so hot after 30 minutes your ass and back are basically sweating....who needs it that hot imo.
If you are not getting fairly hot seats after 30 minutes of driving, I would check the filters and/or get new ones or clean them with a vac....Aaron has a DIY of this on the site if you want because the filters are expensive....I clean them every 30,000 miles.