Reams have been written about the importance of founders that can code--or, in Silicon Valley parlance, the "technical co-founder."

The coder is important, sure. But according to the founders of some the country's hottest start-ups, who spoke Monday at GigaOm's Roadmap design conference in San Francisco, the sheer ability of a founder to code had very little to do with the company's overall success--if anything at all.

The real reason these start-ups have flourished? A Steve Jobs-ian passion for perfect design.

Take Warby Parker, for instance. Some would argue the company is an eyeglass brand: It's not, exactly. Warby Parker is a fashion brand or design company that happens to traffic in eyewear. Its product (glasses) may provide a utility for its users (sight), but Warby's founders will tell you that the viral success of the company had very little to do with its business model.  

"We fundamentally think of ourselves as a design company," says David Gilboa, the co-founder and co-CEO of Warby Parker. "We set out to create a lifestyle brand."

Gilboa was asked about competitors that have attempted to clone Warby's businesses model, and what impact they've had on the company.  According to Gilboa: not much.

"We realized what would be defensible would be a fashion brand," he says. "And design played a big role in that."

Airbnb, which describes itself as the marketplace for unique accommodations, is perhaps an even better example of the power of the designer-cum-founder. Two out of its three founders were art-school graduates with little business experience. 

Today, the company has raised more than $220 million in venture capital. But when the company first started looking for funding four years ago, the founders' art-school pedigrees were met with skepticism. Joe Gebbia, Airbnb's co-founder and chief product officer, says that after initially meeting with 20 investors, none were willing to offer his team cash--largely due to the team's lack of business or technical experience.

"People have a hard time understanding that a graduate from art school can run a successful business," says Gebbia. "If you look at the role of designer-founders over the last four years, it's changed quite a bit."

So what happened? Gebbia believes that we're in what he calls "the third phase of the Internet," which has has place more emphasis on uniting form and content through elegant design. In the 1990s, he says, the problem of the Internet was access--simply getting online, which AOL and other brands solved by the early 2000s.

As access became less of a challenge, a new challenge arose: as the number of people with access to the Web grew, chaos online increased as well. That's why social networks (including Facebook, MySpace, and Twitter) became so popular: they offered a platform for people to make sense of the potential for connection with the thousands, if not millions of other people on the Web.

Today, Gebbia believes we're in the third iteration of major Web challenges. Namely, "how do we use the Internet to connect people in the offline world?" Ultimately, Gebbia believes good design can solve that goal.

"Design has been traditionally an afterthought," he says. "What's unique is that design was baked in from Day 1. I think that what we've seen is this shift to design becoming less of an afterthought and more about being at the front of how people think about solving a problem." 

Even Kevin Systrom, the founder of Instagram, likes to say that Instagram's success was made, in part, but the app's ability to "make sharing fun," as he puts it. But speaking Monday, Systrom noted that good design and positive user interaction may have been the ultimate driver of Instagram's success--not to mention its billion-dollar exit.

"We believe that user experience is what makes people come back time and time again," he says.

The idea of "connectedness" also plays an important role for today's start-ups. Because there are simply so many customer touch points--between Web, retail, and apps--design has become the uniting element that ties these portals together. 

Yves Behar, the designer and entrepreneur behind Jawbone, points towards this idea of connectedness as a major driver of design's recent significance in Silicon Valley.

"It's a really interesting time for design," he says. "Connectedness--the fact that these devices are connected to my phone, my life in general--forces businesses to think through and through about the experience, the design, the look and feel...about their identity."

"When we think about connectedness, essentially that's what design is," he says. "It's connectedness between all these disparate parts, which is really the job of the company to pull together into a clear offering, into a clear engagement with their users."