monitors : Fostex vs Samson and stupid questions

Hi everyone ,

I m looking to replace my so called home studio sound system ( logitech sound system attached to my main pc) for some more serious monitors.
First question is : why most of them are two ways and not three ?
Do I miss something here and can I go simply by a pair of two ways ?

I read in the community some good comments of the fostex PM$ mk2 and some of you recommand samson ..Those two brands are exactly what I can afford and some extra comments will be welcome to take a final decision

Thanks everyone ,