I'm not a programmer, but I'm intimately involved with every piece of UI across our product line as well as our marketing sites.
Some of the UI I design myself, some I work with other designers on, and other bits I give advice, feedback, and guidance on.
I also write the copy on all of our sites, and I'm involved with most of the copy in the apps themselves as well.
I hired DHH as a programmer (and then made him a partner) because those were skills I didn't have. I've done some PHP programming in the past, and I met DHH when he was a PHP programmer, so I was able to evaluate his talent at a very basic level. Beyond that, however, I liked his business mind and general approach to things - they were closely aligned with my own.
I hope this helps explain the dynamic a bit. Let me know if you have any other questions.
BTW, I sincerely meant no disrespect. I've been following 37signals since the homepage was the manifesto (http://37signals.com/manifesto) and am a great admirer of the 37signals' bootstrap business philosophy which I think is a healthy counter-weight to the VC-centric Silicon Valley mindset.
I just wanted to clarify my skills/role for people who were curious.
I think it's crucial that anyone who designs interfaces for the web understands how to design and code in HTML/CSS.