Well put. There are many services, like Mailchimp, that allow you to send a portion of your messages before sending out all your invites (basically an A/B test before unleashing ALL your email with one untested subject line). I don't think startups always think through their open rates to the extent they should.
The body copy is a whole different story, but you nailed that in your post.
A/B testing is a great thing to do with email. On the point of Mailchimp, they also allow you edit the little preview text box - this is what shows as the preview snippet in many email programs and is a good place to remind the recipient what's going on (very briefly, though).
Cool, thanks. I actually don't use the service as of now, but I've been over some of the features. I will probably use that service or a similar one in the near future.
The body copy is a whole different story, but you nailed that in your post.