I think ideally the founding team should have all the necessary skills to create whatever product the business is building, without relying on anyone external. For a web app company that means at first you're DBA, SysAdmin, Programmer, Designer, Customer Support, Sales, etc. As you grow you hand those roles off to others. Web design is the only thing I'd risk letting someone external handle, but even that can become a bottleneck if they're unavailable and you need to make changes quickly.

I also think you should work to become really good at something. If for no other reason then it's hard to build respect from others if everything you do is only mediocre.