It's all about the marketing. Kolb kept a good working relationship with the coaching staff and owners in Philly when Vick beat him out last year. He didn't throw a fit, he wasn't a pain in the ass to the Eagles. I'm sure, at some point, they came to him and basically said, "Vick's our guy, but if you work as a back-up, we'll do everything we can to get you a starting job next year somewhere." He played ball, Andy Reid toots his horn, his agent does his job, and he's the most sought-after free agent QB in the league. The Eagles win and so does Kolb.
What about Vince Young? We can all answer that one. What about Orton? He wasn't ever pushed to a back-up position. What about McNabb? He's old.
Kolb's not the best of these guys, he was the one best sold.