Ecosee, of course I cannot speak for the whole team and for all the Addon authors. But I didn't want to depreciate your work, everybody who is successful in his own business and makes money from it has my respect.
I think you had a good idea in what you are doing but when looking into your site for the first time it looked as if you are selling
the right to use your own photoblog software
and this is definitely not ok.
In my humble opinion (but I'm not a lawer of course) people should know what they pay for: this is hosting, installation and using a free software on their own domain.
Right now it sounds like they have to pay for the use of Pixelpost without even knowing and this is not ok.
So a solution might be to state out clearly that your software offer is based on a free product and you sell the convenience. I guess the Addon authors won't be so strict as long as their work is still valued.
You know that there is a donation button for Pixelpost and most addon authors have one too?
Perhaps a "professional" plan could complete your product range where you offer a domain package with pre-installed (unchanged) Pixelpost together with FTP and detailed information about the free Pixelpost community values.