Professional gamblers don't play pure random games (like craps or roulette) for a living. They play games where they feel that knowledge/skill have some influence (poker, horse racing).
To take poker, bet sizing is an important factor in play, but it has as much to do with the impression the action makes on other players as the actual underlying odds.
With regards to poker, "bet sizing" in the original article is equivalent to "bankroll management" in poker parlance. Bet sizing within individual hands is indeed a matter of game strategy, but the stakes you should play (i.e. blinds or tournament buyin amounts) is closely related to the original article.
Professional sports betters absolutely think in probabilistic terms -- "I think there's a 25% chance we'll win, the market thinks there's a 20% chance we'll win" etc. Kelly bet sizing absolutely makes sense, though market depth and Bayesian uncertainty also act to reduce bet sizes.
To take poker, bet sizing is an important factor in play, but it has as much to do with the impression the action makes on other players as the actual underlying odds.