It is up to each company to decide its own policies about how to deal with previous purchasers, unfortunately. I'm in full sympathy, however, with people who have recently bought Toast. I had a similar experience with Roxio's PC software, where, in response to a series of emails offering a great bargain, I bought it a couple of weeks before a new version was announced. I was then informed by a customer service person that I had to pay the full upgrade price. What is especially annoying in these cases is that Roxio's people already know that a new version is about to come out, and I could have had the latest version for the same upgrade price, since I had an earlier version of the PC software.
There are two things that drive me especially crazy about Toast upgrades. Roxio frequently has different prices for the upgrades. With Toast 9, they emailed an offer of one price and had a price $20 cheaper if you went through the website. I had to call a customer service person, cancel my first purchase, and then repurchase the software to get the cheaper price. The other nuisance is the mail-in rebate. Last time, I mailed in a print out of my email receipt to prove purchase and received a letter saying that the receipt was not sufficient. I had to phone, spend the usual period on hold, and negotiate to finally get my rebate.