I think the delay or the never never of getting it on the iPad has much to do with the ongoing bug squashing on the desktop versions. I never saw or heard fully committed existence of Publisher on the iPad. the language was vague with an emphasis instead on file compatibility across platforms and common to all three apps.
But, I do agree that seeing the trio on at least the Pro iPads first would have done a great deal of positive marketing for Serif.
The original announcements did seem to imply iPad. In other forums and even on other social media, people were chomping at the bit to leave Adobe. With changes that involve battling an incumbent, you know what you can't buy back: timing, timing, timing.