Jim, your site clearly states that ALL versions of MJ back to MJ 8 qualify for the upgrade, with no condition that they be paid versions. It isn't unreasonable to impose that condition, but you should disclose it up front, not after the fact. (And this isn't the first complaint on these forums about misleading statements.)
So you know... The confusion is because of this:
Media
Center was once called Media
Jukebox. There was no free version then, just the paid version. Then, with version 10 (I believe, I'm going off of memory here), they changed the name of the product to Media Center. This corresponded with a major UI overhaul, rebranding, and addition of support for media types other than audio.
There still was no free version. Things went along like this for a while, where Media Jukebox was the "descendant" of Media Center. Media Jukebox was discontinued and no longer developed.
Then, in no small part due to suggestions from users, J River decided to release a free, more limited, audio-only version of Media Center. They decided at this point to resurrect the Media Jukebox branding. This effectively filled the position of a MC Lite in the product lineup. This new, free MJ product was not directly linked to the old MJ type software, but was a "fork" of the current MC code. The idea was to offer a free product that could then potentially drive users to try the full-fledged "flagship" product.
So... That's the deal. You do get upgrade pricing on the current version of MC even if you owned one of these old, paid versions of Media Jukebox, but not if you simply download and install the current free Media Jukebox product (which would mean anyone could get the upgrade pricing, simply download and install MJ first).
It looks like Jim changed the text to be more clear, but that's the background story.