The lower upgrade price from 11 to 13 would be to buy poser 12 then Poser 13 saves you $50.  How much lower do you think it should be since a lot of people bought Poser 12 and paid more then the current price of $99?  Of course I could complain that I bought Poser 5 and they don't give me an reduced price to upgrade.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13