I think the article's point is that, if you compare banners to physical billboards, then you have the same issue but the billboard still works. So even your theoretical mom and pop store is getting value out of the impressions.
The vast majority of ads for luxury cars, for example, aren't going to elicit an immediate purchase, but still provide value for the automaker down the line.
Obviously the ads have to eventually lead to sales, but an immediate and trackable sale isn't always an option.
In some cases, that may be right, but in general branding begins the first time someone interacts with your product (or even your industry). If I notice your business name on Google SERPS, I am engaging with your brand.
I didn't really use NewRelic for 2 years after I first heard of it, but I did keep seeing them and speaking to them at events, reading blog posts, etc. Eventually, I signed up and paid for the product. What convinced me to do that was the branding work they did before I became a customer.
Even for freemium products, the business builds a brand to encourage people to invest the effort into signing up. Even government services (e.g. in the UK - the BBC, the NHS) do branding work.
Branding doesn't start at the point the customer enters their credit card.
Lovemarks is a good read on branding - http://www.amazon.co.uk/Lovemarks-Effect-Winning-Consumer-Re...
Also, you're not sending me your credit card number, you're sending it to Stripe, or Amazon, or PayPal. Regardless, I think you severely overestimating how cautious people are with their credit card info.
Impression based brand advertising is a different model to click based lead advertising. The former places all the risk and work on the adveriser, the later pushes it towards the publisher. If you run a website that's hugely popular and don't want to waste your resources on other business's ad campaigns then selling by impression is the only sensible option.
What the article is saying is that there's an upper limit on the amount of fraud that can be perpetrated without showing up in other metrics, and at current prices, brand marketers just don't care. Because brand marketers don't care about impressions; they care about P&L at the brand level. If a banner ad campaign drives top line brand revenue, that's all they need it to do.