Its as simple as this: designers rarely program and programmers rarely design. They may be able to do the basics, but when you need serious design or complex programming, hire accordingly. If you need both, then hire both...
I've noticed over the years that the most successful people I've met tend to admit when they don't know something. Admitting their limitations gives them the freedom to hire or ask someone with expertise. So if you want to be successful, admit it...
I recently had a client ask if I could make a simple change to his website or if that would destroy my artistic vision. I chuckled at that and told him, "my artistic vision is always open to change based on my client's needs." There...