Actually, that's not why Doyle died. Joss did want to kill a character like that, it's true. But that wasn't the case with Doyle.
To quote David Fury: "Joss has bandied about, 'I love the idea of putting a character in the main credits as one of the stars of the show and then kill him right off the bat, but in the case of Doyle, he didn't want to kill off Doyle. It just became a situation. The work situation became difficult.... It's hard enough to make a television show without the headaches."
I'm not entirely sure what he meant by "the situation", but I think it's safe to say that Doyle's death wasn't suppose to go down like that. Just wanted to clear that up.