they are nissans with a different badge, e.g. an infinity i35 is a nissan maxima. this is different from lexus/toyota. you can't buy a lexus that is basically a toyota camry, similarly there is no toyota that is a stripped down ls430.
my uncle has had an i30 since '98 and now has 293,000 on the clock. it still goes/stops etc pretty well for a car that old. my only bug bear with it is the short oil change intervals (just 3000 miles!)