Who creates the artworks?

I read an article in The Independent about a row between the two British artists David Hockney and Damien Hirst

“A row is threatening to break out between two of Britain’s most celebrated artists after David Hockney criticised Damien Hirst for the “insulting” use of assistants to create his works.”

(follow the link above and read the whole article)

It rises an interesting question – does a piece of art has to be made entirely by the artist or is it still the work of the artist if he or she hire assistants to do the handcrafts for them?

What is your opinion ?