When we decided to make a change to the Zendesk pricing structure for our existing customers, we tried to be as thoughtful, transparent, and straightforward as possible. Transparent? Maybe you should've given your customers a warning first..? While the letter is certainly worded very nicely (and carefully), it reeks more of damage control than sincerity. The picture with the puppy dog face puts it way over the top.
How do you get more sincere than, "We failed. We let you down. And we apologize."? I'm asking this in all honesty; I don't really understand where you see this as being insincere. Just curious.
This is an apology for carelessness, but the real issue is greed. That is why it strikes me as insincere.