I find it quite normal for a small shop (I don't know the size of Tumult) to try to limit the number of platforms they wish to support. If they use Mac tools for development they will most probably me more efficient supporting the Mac.
Also, single platform toolkits are just so much nicer to use compared to those working on multiple platforms.
Also, single platform toolkits are just so much nicer to use compared to those working on multiple platforms.