As far as I'm aware the most significant difference is that GOG got multiplayer a few months later, and the Steam multiplayer environment is a lot more active - although that's not super important for me.

But does this mean there are other differences - is there the same commitment to update GOG at the same time as Steam for less platform dependent updates?

It has been my experience as a bought-it-prerelease player that the updates have been available on GoG more or less simultaneously with the Steam releases.
I do recall some instances where there were slight delays (hours, maybe up to a day?) which lead to dramatic cries of grief and tragic moaning that life was dark and empty. The usual.
All of the major, minor, and intermediate patches have been up on GoG, including the beta channels.

Updates in GOG are much better than the Steam ones, because you have total control of when you want to install them, on Steam you don't have this control, the game will be updated as soon as you stop playing offline. With GOG you can even revert to older game versions, a thing you cannot do in Steam.
Currently MP features of NMS are reduced because there is no interchangeability between Steam and GOG for MP.

And one more thing: People on Steam forums seem to have an average IQ of 70...GOG forums are much more qualified, and not just for this game.

Actually, it appears you can. At least people are reporting playing on Pathfinder or Atlas rises versions.

Yep, with some elaborated tricks not supported by Steam you can do that...

Thanks guys - purchased :)