Chelsea and the youth team...I honestly don't even know why Chelsea or Man City have a youth team. All they do is train them up to play in the Carling Cup (maybe for 1 round) and then either go out on loan or get sold. When was the last time a Chelsea youth player broke into the team and actually stayed in it? They will always go for the big names, and players with the reputation and transfer fee will always get played ahead of youth.
So these players get top level talent and exposure that usually earns them a move to another decent sized club - I wouldn't they're doing that much harm to young players. Inevitably 95% of them won't be good enough to play for Chelsea but as long as they can get decent development and a route that could lead them to a reasonable club their spell at Chelsea will probably be seen as beneficial by them.
Occasionally you'll get players like De Bruyne who don't get a chance in spite of being quite clearly good enough or thereabouts but mostly players who leave are simply not good enough.
They loan them out without much hassle and have some good satellite clubs too.