There may be more successful Windows Phone developers out there, but none of them are as open about the performance of their apps as Elbert Perez, best known for Scribble Defence and Impossible Shooter.
He has just tweeted that he generates between 1.5-2 million impressions per month from his 14 apps, but did not reveal the earnings this generates. We can however speculate that in good days it will be closer to $10,000 per month, which is a reasonable living wage, and in bad times closer to $1000, which is not. It is likely the true number is somewhere in-between.
While one may speculate that he could have earned more on iPhone or Android, it is also very likely his games would have gone unnoticed, making the real good news that it is possible to make a living wage developing for Windows Phone.
See his site here.