If this was a real money gambling app, then either (a) the odds were stacked against the player by 1-2%, or (b) there was rake (for non house games like poker), so there was no need to charge for the client.

If you think about it, that's how FTP or Poker Stars works. Download a free client, even play for free for play money, earn money on rake once they convert to 'real money' players.