I've seen a few bounty campaigns in my days. Quite a business model, I tell you, fits in just great with the ICO. It's a great way to start off a successful ICO campaign.
It is not compulsory though, as there were lots of successful ICOs without Bounty, even though it helps a lot.
Those ICOs were built w/out bounty campaign hopefully their clients wouldn't complain, it's not such a perfect instance of avoiding bounty campaign.