on another note , you could argue apple has as much knowledge as sony or Ms did when they enterd the consoel market but this would not be entirely true.
those companies both made pc and console games prior to thier first consoles, but that aside they also had something new to bring to the market with thier consoles.
when teh PS1 came out it brought a "mains tream" appeal with it's game designs mainstream being, not casual but at the same time not hardcore. they in essence filled a gap with their console , reagardless of what exprience they had , but it helped a shit laod that they did indeed ahve exprience making pc games.
MS , beyound spending bilions into R&D for thier consoel department , also ahd huge exprience with pc game software. on top of that they filled another gap in the market, thier console targeted the hard core crowd , while not as big as the casual or mainstream at the time , hard core gamer crowd has tripled in size in the last 8 years , (which is how MS was able to pul off getting second palce in US sales)
that said ther are no more gaps in the market, so until oveall gamer population goes up drastically , the market will not and can not support a 4th contender , as i stated in other post.