Is design important?

Lately I made a small web application for a client, showing their data on a spreadsheet-like page. I felt the data were the most important part for the app, so I made it full width with a flexible grid. I also hid the links in a dropdown menu with some quick CSS3 styled lists. The design fully responded to the functionality of the page, and the client would surely be happy.

Or so I thought... Until one day, the client sent a screenshot of the page, as it appeared on their browser. The browser, was old, really old. And my page looked so broken :(. The dropdown menu was rendered as a normal list, taking half of the screen, and pushing down the data spreadsheet. There were scrollbars on the page, whereas my design had excluded them.

I offered to fix the page, but the client didn't mind. They had accepted their 'reality', that the browser on their work computer was really old and got used to the page as they saw it. And their company is quite big ...

That experience made me think, is design important? Do we need to spend hours on small details when the client won't even notice them - or their browser won't let them? But I love design, and I pay a lot of attention to detail. However, the app is not for me, but for the client ...