He's referring to those super long letters that are sent out, & they do work. The trick is not just in the copy, but also in the list. A good marketer will choose 10 lists or so, each targeting a slightly different demographic. To these lists the marketer will A/B test and see what the conversion rates are. After finding the best conversion rate, the rest of the campaign will go to the list that performs the best. After years and years of iterating through hundreds of demographic segments & lists, different copy/headlines, & even minute details like whether to have a hand-written note inside, whether to have a "P.S." message, whether to use the word "Guarantee" or "No-Risk", etc. (These little details actually make a repeatable difference in conversion rates)

After all this, a particular company will know exactly the demographic that buys, exactly the headline that grabs attention, the copy that gets people to keep turning the page, the post-script message that increases conversions, etc.

This kind of marketing has been perfected, as the author says. A good direct-mail marketer will get a conversion rate of 5%-10%. There are some books you can read to get at specific numbers of different campaigns... This is one of them http://www.amazon.com/Getting-Everything-You-Can-Youve/dp/03....

To get fundamentals and theory foundation, drop the "internet" part of your requirement. The internet is just another way to connect people.

All successful marketing comes down to a fundamental understanding of people, how we like to be spoken to, what captures our attention, and what messages stick.

Read my notes and excerpts on some of these books to get an idea if they're what you're looking for:

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Small is the New Big - by Seth Godin

A "best-of" collection of small essays about marketing. Seth writes in general terms meant to give you perspective, change the way you think about marketing, and inspire you to actions, no matter how small, that make all the difference. Read anything by Seth Godin (as others here have said), but this is his best overview.

http://sivers.org/book/SmallIsTheNewBig

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Made to Stick - by Chip Heath and Dan Heath

A deep analysis of what makes certain ideas or stories memorable.

http://sivers.org/book/MadeToStick

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You, Inc - The Art of Selling Yourself - by Harry Beckwith

Harry Beckwith is amazing. Read everything by him. This is just his newest. He's the best at reminding you how basic human consideration translates into marketing.

http://sivers.org/book/YouInc

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Getting Everything You Can Out of All You've Got - by Jay Abraham

Jay Abraham is an absolute marketing genius from an angle the others here don't cover. This gets you into his mindset, seeing profitable aspects in your business you never noticed before, and how to communicate them to your audience. Sorry I don't have notes on this one:

http://www.amazon.com/dp/0312284543

http://www.amazon.com/Getting-Everything-You-Can-Youve/dp/03...