My understanding is when they fly you out, you're pretty much a shoe-in and now they're letting their devs have a shot at trying to interview, while getting a feel how you work with others. i.e. are you sane or will you eat on of our disposable dev's face?
This was not my experience. I did not get an offer after being flown out and spending the day interviewing. I did not do well in the whiteboard coding, but I found the people I interacted with to generally be interested and smart.
