According to the Steam news, the latest version there is 1.5.4 from June 20, 2017. According to the Changelog entry of this GOG forum, the latest version is 1.0.3 from September 12, 2016.
Is it correct that GOG is 9 months behind Steam as far as patches are concerned (and apparently 1 DLC: London Tower)? And if yes, is there a reason for this - have the Steam patches after 1.0.3 all been pointless or faulty, or are there business reasons?
To put it simple: Why should I get the game on GOG and not on Steam (except that it's currently cheaper on GOG)?