MailChimp's voice & tone guide at voiceandtone.com does a nice job of explaining the 'why'.

Thanks for the tip. I can recommend this guide after reading it. It does a nice job of defining the right tone of voice in success messages, account creation, press releases, legal content and failure messages. It starts with the user feelings and shows an appropriate response.

Edit, added direct link: http://voiceandtone.com/

There needs to be a way to filter out the most successful ones. Such as filtering or sorting by open rate or click through rate. Otherwise you're assuming they're successful just because it's a popular brand which is not always true.

How would that be possible? You can't compare across brands, because as you said, some are successful because they're a popular brand, which would affect CTR and open rate too.

I'm somewhat hesitant to post this link since it's a bit self-promotional, but I wrote up my thinking about what makes good product copy: http://sonyaellenmann.com/2016/03/how-to-describe-your-produ...

Well there is this I found with a quick search: http://blog.hubspot.com/marketing/good-copywriting-practices...

Essentially, use a hook, get to the point, don't be too wordy, be impactful, and make a connection.

I'm not even sure if these examples are that effective. What makes them effective? If the measure of success is whether or not one actually reads the copy, then for me the best approach is to right it like a personal message. In that case the success of email copy is predicated on deceiving the recipient...?

IMO, more startups would be struggling to write any copy at all before it's about effective copy. So I can see this being very helpful as a starting point.