Loophole engaged: OP says nothing about these characters not being confirmed! Also, proof has to be true, but explanation may be silly! Well, what we could do about it...
So you may have heard Capcom allowed Mega Man solely because of money. That's not true though! The actual reason for that is that the primary game in which Mega Man fans could make him fight is going off the shore, and they wanted to keep them calm! Also, Sonic got in again as a Yoshi replacement, because now that he's visited Yoshi's Island he can be one, and Yoshi couldn't get there yet, for some reason. Another confirmed character is Pit. Guess what, Smash fandom doesn't like "walk-off" arenas too much, so appearance of Pit was guaranteed. A recent newcomer is Rosalina. She has been included so that Nintendo has one more spot to shove the spoilers about something concerning her right into your face - that's right, I mean her Smash profile page. Luigi would probably have been thrown out weren't it for Year of Luigi, and Mario too - after all Luigi's his brother, so absence of Mario would be a little surprising. Samus got in because while she's in her armour, everybody can imagine their favourite non-included character in it. This was suggested by Reggie wearing a Samus pin closely to his announcement that he could possibly be playable in Smash Bros. Finally, we can say with whole certainity that Olimar's and Marth's presence was there to advertise... the DLC for their franchises' games containing them.