[whpalmer4]

Fantastical makes calendar software. It's not a big deal for them to write some glue code that makes their product continue to work in the new environment, if they didn't already have it (they probably needed to write it anyhow).
In Omni's case, it's pretty far off the beaten path, supporting a feature that has long outlived its intended purpose. I don't see any reason not to take both companies at their word here. Supporting it is a good investment for Fantastical, and not for Omni.