Yes, I have confirmed Leopard is a requirement.
Normally Phase One does go back at least one major OS in compatibility requirements.
The sub level differences between 10.4 (Tiger) and 10.5 (Leopard) are substantial however. And while some of the build may have been started for Tiger, when Leopard arrived it clearly presented challenges. I think the time it has taken for us to get the software to market demonstrates that quite effectively.
I think a decision has to be made at some point whether you're going to launch by a certain date, which is already way late past expectations or are you going to push out the delivery date by even another 6 months or more. If we had Leopard and Tiger compatibility, by the time we had both and ready for release it is quite likely that Snow Leopard would be out, meaning even more delay. I would expect that major OS revisions are extremely traumatic for a software development team and that it would be easy to get behind and then never get caught up as OS revisions keep coming and you have to to keep writing.
All this said, Mac OS 10.5 has been out over a year now, since October, 2007. And we are not the only MFDB company, nor the first, to have this restriction. Potentially there are workarounds I would think, running a dual boot with multiple OS's, dedicating a cheap Mac for print jobs, etc. I know these aren't ideal. And I do absolutely agree it sucks about having to upgrade an OS before you want. I am not a fan of that either. If there was a way for our development team to go back to Tiger realistically, they would have done so.
Regarding the 4.5 download - it is not a hoax, it should be available today. There is no issue that means it's going to be another 2 months, etc.