I've learnt that op-amp can be used as a comparator ,so why there are components that they are reffered to as only comparators not an op-amp ,for example in isis proteus simulation program there are separte library for both op-amps and comparators.
Comparators are run in saturation or cutoff type modes, i.e. they're either on or off. Op amps, while they can be made to operate like a comparator, usually operate in their linear region providing amplification and filtering. Thus two different operations and two different behavior models.
Correct, but also be aware that comparatora often have open-collector (or open-drain) outputs, so comparator outputs can be connected together in a wire-and configuration. Op amps drive their outputs either direction, so op-amp outputs can't be connected together without disastrous results.
Not necessarily. You don't need feedback resistors for comparators in general but they can be used to add hysteresis in the response. Op amps in active circuit design almost always have feedback resistors and resistors on the + and - inputs.