Need to be both in order to be successful. There are many great photographers, but would starve if they actually had to sell their work to feed themselves.
No you don't at all. There are heaps of crap photographers out there (many "accredited") doing well because they sell and an experience which is great even though the product is naff. In the domestic market people buy an experience as much as they do the photographs and in many cases more so.
You need your work to sell to be financially successful that can come three ways.
1) Crap photographer but great sales person. The salesman in the photographer sells the experience.
2) Exceptional photographer crap salesman but the work is good enough to sell itself.
3) Good photographer and good salesman.
1 and 3 are the most common. 1 is the scenario the industry loves to hate since it "degrades the profession".
2 is more rare since most photographer's work these days in the domestic market has very little uniqueness to it. It doesn't matter if you are just good when there are countless other people at the same standard in a saturation of supply.
Define "great" photographers. Being good at photography and making a living from it don't necessarily go hand in hand.

(24Lii, sigma 50A, 135L), and for the other ends of the spectrum, sigmaEX 14mm2.8 and sigmaEX 100-300F4.
