Believe it or not they already announced a Saw VI as well...
I remember in the 1980s when franchises like Friday the 13th, Nightmare on Elm St. and others were churning out sequels close to every year but I don't recall any movie series having a movie come out 6 years in a row.
They're milking the Saw franchise until it's completely dried out and nobody will want to see it anymore.
Sometimes it's good to pop out 2 or 3 movies in a franchise while the characters are fresh and the actors are all available to play the roles... but there's definitely something to be said with walking away for awhile to build anticipation for the next movie should there be one in the making later on.
In much lengthier examples than what I mean, Indiana Jones came back after a very long layoff and did great box office business. The rumored Ghostbusters 3 movie will be huge if it comes out even though the second Ghostbusters wasn't exactly great.
Freddy vs. Jason did well partly because of the battle concept but also partly because there hadn't been a new Freddy movie in 9 years.
-Rp