well, if you look at the haynes manual, you will notice that when it shows how to change the tire, the pic is off of some old junker, not our cars, so they are probably using some archived photos from the 50s (probably a little off but you get my point 
the plugs they used are probably not platinum plugs, therefore getting diffrent ware charictaristics. also (I believe) that the plugs in the manual show how to diagnose what your engine is doing, (running lean, rich, burning oil, ect) not a worn plug. you got a 98, so probably less that 30k miles, so you are good, if you are going to replace your plugs, use the ngk platinum (stock) plugs, but go one heat range colder (6) and your car will run alot better (not like, hey I put this header on and can do a second gear burnout), but *slightly* noticible.
the plugs they used are probably not platinum plugs, therefore getting diffrent ware charictaristics. also (I believe) that the plugs in the manual show how to diagnose what your engine is doing, (running lean, rich, burning oil, ect) not a worn plug. you got a 98, so probably less that 30k miles, so you are good, if you are going to replace your plugs, use the ngk platinum (stock) plugs, but go one heat range colder (6) and your car will run alot better (not like, hey I put this header on and can do a second gear burnout), but *slightly* noticible.
