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.)

What about Bronstein? He drew the match with Botvinnik, so he should've been at least 'co-champion'. Also he played a lot of computer chess.

Yes, and Leko drew with Kramnik after losing the last game :(