Call me cynical on top of being a Spider-Man fan but there's two reasons for why will be getting Amazing Spider-Man three times a month: First, the obvious one is that Friendly Neighborhood Spider-Man and Sensational Spider-Man have been in a sharp decline in terms of sales because more readers would rather buy Spidey's flagship title than two spin-offs, at least according to Marvel. Of course, the other two titles have been desperately trying to find their own style in comparison to ASM, plus ASM gets better press to begin with. But the other reason is that I believe that Marvel is really, REALLY worried about the aftermath of "One More Day" which is not only JMS last story on Spider-Man (hooray!) but it is also rumored that it's the story that will somehow dissolve Peter's marriage to Mary Jane. Having a writer who had given an, admittedly, much needed boost to the title AND getting rid of a pairing which, by now, is on the same level of Superman and Lois, will likely result in very big sales drops for Amazing. Changing Friendly Neighborhood Spider-Man and Sensational into extra issues of Amazing Spider-Man could be a way of stemming off this potential sales drop. And with Amazing Spider-Man selling three times a month, you can be sure that Marvel, by totaling up the sales for that month, will proclaim Amazing Spider-Man "The number one comic book in America!"
So, I guess Marvel has officially revealed what happens to Mary Jane--she replaces the Black Cat as the superheroine who tempts the superhero! Of course, anyone who read the Free Comic Book Day by Dan Slott would've also learned this.