My opinion is that it comes down to traffic and conversions. Most people don't know how to drive targeted traffic, so they get lots of bounces and very few conversions. If someone isn't interested in what you sell, but you pay for a Google ad that isn't a good fit, then you aren't going to be very happy with the lead and sales results.

Going one step further, if your site isn't designed to generate leads and sales, then you'll likely be disappointed as well. Lots of designers design for aesthetics not conversions which is a big mistake. Every design should start with goals in mind, and this influences the information architecture, the design, and the copy which ultimately is what will lead to sales and results.

So it comes down to two things: 1) Making sure you can drive targeted traffic and not just traffic (although traffic of any sort is a big problem for most people and 2) Designing your site for conversions, not just looks.