I'm mildly surprised that we're still having this conversation. Feels like the late 90's with the same "marketshare" arguments.
I tend to choose Mac only developers even if their price is higher than average (Omnigroup) because I do want strong focus on leveraging the unique capabilities
of my chosen platform.
To me Serifs choice makes sense. The Mac platform has cried out for a capable vector program since Adobe swallowed up Freehand. There's much more to delivering
software than writing code. For every platform you choose at a minimum you're looking at the time to write the code, time to QA test the code, expenses in marketing the app
to different markets and the costs of supporting users. With Macs you have a fairly insular brand as a developer. You know your GPU are going to be either AMD or Nvidia based
product. There's not a whole lot of hardware surprises or funky configurations.
Will Serif extend the product to Windows? I'd say it's likely but there's nothing wrong with growing the product and the brand on Macs and when the suite is very stable and mature moving to additional
platforms or going mobile.