Also, why does the bros. discovering [or stumbling upon or whatever you want to call it] the Mushroom Kingdom preclude any possibility fo them being there before? Oh yeah, picture this in the SMB manual: "Mario heard about the Mushroom Kingdom's plight, and since it was his homeland that he didn't remember, which we'll tell you about in another game in 10 years, we just won't bother with Mario's history anyway, because this passage was too much info to put in the manual and we don't really have Mario's story established yet." You think the writers thought they needed to tell you that Mario was from the Mushroom Kingdom? They assumed no prior knowledge of Mario on the player's part and they didn't know what was up with Mario anyway. So, they just put a simple, undetailed story in the manual. Then, later, they decided what Mario's history was, and they put it in YI. It's not really possile to create a whole story line for Mario beacuse the people who make the story don't have it all worked out anyway.
It sure gets boring having the same signature all the time. See what I mean?