Ultimately the only people who can differentiate between "Generic Notes App #138" and Vesper, are people who have been trained to care about details that most people don't care about, and that's a very small market. Most people care far more about the fact that an app syncs to Dropbox, or lets you set a background picture, than one that animates screen transitions in exactly the right way.
I'm sad to see another indie Apple-ecosystem developer close down, but I saw this coming as soon as Vesper was announced, and I'm not in the least bit surprised. Unfortunately too many of the Mac/iOS old-school community go for the "I know best" + waterfall development approach, rather than trying to figure out the product-market fit. I say this as someone who has worked in both an old-school Mac OS company, and startups who have been far more agile.
That's what you get when your app design/development philosophy is based on Steve Jobs.