Squad\'s game Kerbal Space Program has the options for buying it from Steam or from the develop site directly. Buying from either doesn\'t require acquisition or play from the other; in fact, in their case you don\'t even need Steam running to play the game once you have it.
Since Starmade is already being purchased from this site, it\'s quite possible that when Steam hosts the game that people will still be able to get the key more-or-less the way you already have, while those who have Steam can choose to get it through that.
As SnakeMittens pointed out, KSP is not the only one doing this. Many games are going the Steam-Or-No-Steam options to give convenience of choice.