Okay, a few hot words here so I'll interject some thoughts.
I don't think anyone is suggesting new writers choose hackery over writery routes but a canny writer, in what's essentially a marketplace, can help his chances (as in any other business) if they offer what the customer wants.
Example: The vogue for sketches seems to be short and concise. So a project featuring 8-minute blockbuster sketches is realistically going to attract less interest than one built around market trends.
In balance, I think Tim is worried that writing to trends and requirements involves compromise. He's right in that no writer should chase the golden egg. We should write true to ourselves. But consider that many professionals write to a brief, which is basically a list of requirements the customer expects to be met. Plus, most scripts are revised / edited / rewritten to tailor a producer's then a broadcaster's requirements. And the commissioning process is, by its nature, self-selecting: all broadcast scripts will meet the broadcasters' current requirements. The difference being some scripts were conciously written with requirements in mind, some were written without regard to trends but fortuitously met them anyway.
Does this mean that awareness of trends compromises a writer's integrity? Unknown, but it will more likely compromise their bank balance.
Lee and Tim both mentioned the key element to this debate: voice. You can teach scriptwiting but you can't teach voice - the one element that stamps a writer's identity throughout. Lose the voice and you lose a writer's integrity. Maintain the voice and the writer can be proud of any output.
Finally, let's get some perspective on what we're dealing with here. We're working in a disposable medium. Today's shit hot is tomorrow's shit. I don't imagine we'll see 25th Century folk gather in awe around an original Fawlty Towers script, in the same way they'll still be gathering around the Mona Lisa. When we look at the moment in time we've been allotted, our chosen medium, our goal (laughter), we'll realise we're all in the same business of trying to hawk our words. The only difference is in the choice of words we use to distinguish between our hawking and the hawking of others.
Maverick, Twat, Hack, Writer - I'd gladly embrace all those terms if I had a show on TV.