Getting back to the original topic -- I checked The Stand, which is the only title I have that I know for sure is going to be TTS disabled, and it still works. It may not be the best example, since it's not currently available, but the holding page for the Kindle version tells me that "You purchased this item on July 11, 2008" so I'm guessing the ASIN will be the same. I did download a couple samples in the past few days, so I have connected to whispernet recently.
I would be really surprised if Amazon applied this retroactively anyway, and I find this whole Orwellian idea of what Amazon can do to our content sort of overblown and paranoid.
Also, listening to the first page of The Stand in TTS reminds me of why I would never choose to use TTS
It's awful, and anyone who thinks it's a valid substitute for a real audiobook needs to have their ears examined pronto.