Why do people buy separate camera, GPS, Ipod, music player, instead of buy a Smartphone that has all of those?

I see many people buying separate camera, music/video player, GPS for their car. It sounds like a dumb idea buying all those separate things when they can just buy a really good smartphone like iphone that good camera with like 8 MPs, music player, Phone Based GPS and all that, besides it would be portable to carry just one device instead of million devices. Is it that most people have money or they are not smart enough? Thanks