Snake and Sonic was suppose to be in Melee, Kojima and the Sonic Team Creator are close friends of Sakurai. They approached him about putting their characters into the game but he couldn't because Melee was far in development. That means that Sakurai already planned out who he wants to be in the game and no amount of polls will influence him. Sonic and Snake inclusion in brawl had nothing to do with fans, he included them because he is friend with Sonic Team and Konami requested them to be in the game.
Look at the pattern of how the 3rd party characters are selected. What does Sonic, Mega Man, Snake, and Pac-Man have in common with one another? They are all Legacy Characters that changed and shaped the gaming industry. Sonic was the game that really put sega on the map and it was the game that challenged Mario and the Nintendo brand. They were bitter rivals, so Sonic earned his spot. Snake was pretty much the first stealth game released on the NES and Snakes Legacy carried over to the PS1 era and Kojima decided to bring the Legacy back with Metal Gear Solid Twin Snakes on the GameCube.
Not only that Snake Eater came to the Nintendo 3DS, yes Snake earned his spot on the Smash Roster. Then you have MegaMan, he was the first Console only release Arcade 2D Platform shooter on the NES and his legacy has spread on both Nintendo Consoles and handhelds. So yes MegaMan earned his spot on the roster, if you thought fan demand had something to do with his inclusion, than you are naive. Sakurai said that he won't pick any 3rd party character to be in the Smash Brother roster. They have to be the right fit and represent the Nintendo Legacy properly.
Pac-Man inclusion had nothing to do with fan demand because it was a no brainer of his inclusion for the fact that Bandi Namco was working on the game. Pac-Man changed Arcade gaming so he earned his spot regardless. Yes, when it comes to including newcomers GENO could be selected but not before other more deserving characters.