It doesn’t matter, the option is there. Apple reserves the more technical betas to developers and they get all the support they need. The public beta is a preview for everyone else and you will not get any support. It is in Apple’s interest to make the process not more complicated when they have no intention of helping anyone. The fact is that Apple doesn’t normally use IPSW files and I see no reason why they should do it now, even if you find it practical.
There's a hole in your post though. If anIPSW is too technical for a person using it for the public beta, then why is it available for the general release? If your 'get out' clause is that there is a document on how to use an IPSW, then that could just be used for the public beta too. Additionally, Apple don't widely advertise the public beta, which means people have to be looking for it or on sites like this. Those people are not the same as general public.
Im just bemused by the people that have posted contradictory information in this thread.
Oh and by the way, my bug that I had, I no longer have since I did a clean install (via 8.4), then restoring to my backup of 9 PB 3, so if anything, there's a valid use case for letting us access IPSW's on public beta. I've now wasted someone at Apple's time for a bug that wasn't affecting anyone else, which was resolved by doing a restore.....