I think what really makes it work is the way its done. It's funny, but considering what we got with the first 2 series and even for the first xmas special, as Brent continued to sink lower and lower just for fame, a happy ending was the last thing that could be expected. But I think it was handled with just the right amount of care to make it truly fit and not seem like a cop-out, as it so very, very easily could have done.
And you know last night how I was planning to rewatch those specials next week? Yeah, being reminded of how awesome they were has forced me to make a change of plan!