I think La Bourdonnais deserved to be in the list. Wasn't he the first champion, as we would consider by modern standard : a player who won his supremacy over the board against valuable opponent(s)? Didn't he won the first true match in history (I mean against a strong opponent, with media coverage and with all games still enjoyable today)?

Yes, you are right, but our selection from pre-1886 is subjective anyhow. http://en.wikipedia.org/wiki/World_Chess_Championship#History_of_the_world_chess_championship

What about Topalov?

Topalov is No1 today http://chess.liverating.org But as you can see, our list contains undisputed and classical world champions (from 1886), and nobody from FIDE champions in split time (1993–2006.)