The whole "It's between Ribery, Messi and Ronaldo" debate was invented by Ribery, Bayern and the different voting system for the UEFA best player award. In reality it's much more open: People tend to forget how this is voted for. It's not a list of three players out of which the voters pick their favourites. Everyone can pick whomever they like as their top 3, with different points given for the respective places. There will NOT be a second round of voting, with people having to decide between the top three candidates, which is what saved Ribery's head for the UEFA award (he wasn't the clear first place after the first voting). Several voters will choose other Bayern players like Lahm, Schwein or Robben over him. So Messi will almost certainly get more first place votes than Ribery. I suspect Lahm for example, who would be Team Ribery, to vote for Schweini, and Löw for Lahm (or maybe even his favorite Özil).
Also, it is quite unlikely many people will leave Messi out of their list, while this could easily happen to Ribery. So here is where Messi will grab loads of points from second and third places, while Ribery might lose those to Ronaldo, Bale, Neymar, Iniesta, you name it, from voters who don't value the treble as much and just pick who they think are the three best players.
Then, two thirds of the voters are players and coaches. Those tend to favour Messi, a lot. Just look at the quotes from Ibra etc after the UEFA gala. They don't care about injuries.
Also, let's not forget this is not a UEFA voting, but a FIFA voting. Players from South Africa, Africa, Asia and so on might not value the UCL as much. And it is true that Messi attracts loads of votes from there because he is the biggest football celebrity, because of his reputation and his status as the best player.
And anyone in doubt shoul check out last years' votes - it's not like it's been a close race. Messi gets so many votes that it takes some really big player to beat him, and frankly, that's not Ribery - maybe Ronaldo if he managed to win the world cup or something.
Now as for Messi. The arguments about Messi's form and injuries might or might but be true. But before Messi came onto the stage, no rational arguments in the world could have argued that there would ever be a player who grab the award four times in a row. Messi has changed everything. He is not regarded as a player like the others anymore, but like a phenomenon, and people treat him this way. Many peoole vote for him not because he's had a great year, but because he is freaking Mozart. That's why the award will strange to vote for after Messi retires, as the next winner will hardly measure up to him.