Of course there will be time in between for sales to increase or decrease. It pretty much determines on a company's sales if they can afford to make another game system.
yeah I think it's been said already, PS3 has only been out for a couple years now and it'll take awhile for the next gen gaming console to come out. PS1 came out at the end of '94, PS2 was released at the end of '99 beginning of 2000, and PS3 came out in Nov. 2006. there was five years between PS1 and PS2 and six years between 2 and 3 so it'll be at least another three years before we see PS4