Ronaldinho was your stereotypical luxury player - he didn't really track back or do much defending but he was worth accommodating because he was so damn good. Messi on the other hand, will work hard for the team (although seemingly less these days).
When I said work ethic, I meant generally speaking though. I might be being harsh as I can only judge what I see on the pitch really but I find the fact that Ronaldinho let himself get so out of shape disappointing. I don't know to what extent injuries played a part - the loss of pace was a big blow to his game - but even so.