I don't know this industry niche well, but I'm guessing Rafflecopter is a chief competitor. I think if they see this blog post, it'll rattle their knees a little :)
The flip side, of course, is they also don't guesstimate future revenue from new customers attracted by likes generated by the promotion, or from increased engagement (or revenue lost because people made purchases they were going to make anyway but at a 10% discount, or because they were annoyed by the promotion and unsubscribed). Even direct marketing often is more data alchemy than data science :)
The $13,000 figure is only applied to the new customers they picked up with their promotion, based off of current LTV figures JewelScent has.
Your second question raises a good point, which is hard to substantiate either way given the youth of both JewelScent and ViralSweep as companies (i.e.: we'd need more data and more time to know for sure). The priority for both companies is to deliver a great experience for our customers; the needle will continue moving in the right direction if we can continue to do so. It's easy to get bogged down analyzing data whose impact is dwarfed by executing on the 'Big Picture'.