US media adapter firm Roku this week more than doubled its share price, as doubts about its credentials as a platform player were swept aside. The company re-iterated its claim to be a “mostly” software player, on the back of astonishing growth in platform revenues at its results last week, and on the signing of the Philips TV brand, now owned by Funai Electric, to its recently upgraded TV OS. In essence, investors are starting to believe the “platform” story, and where Android has dominated set tops and a handful of TV platforms, Roku now appears to dominate smart TVs in the US and is starting to globally. That means its operating software will bring in from licensing fees and…