I think Foster truly could become a United and England great. I don't know why people think Fergie likes him because he is English. Fergie is Scottish and has no interest in using the Utd squad as a training ground for the England team. And you could hardly say he is doing it to appease the English fans, because the English fans seem to give Foster nothing but stick.
Fergie has observed day in day out two of the all time goalkeeping greats (Schmeichel and VDS, neither of whom were English).
He is clearly seeing similar things day in day out from Foster. Obviously Foster has failed to truly compose himself in the Premier League thus far, but once he has a good run I think he'll be unbeatable.
I can see no other reason why Fergie would put Foster ahead of Kuszczak, who is a great goalkeeper in his own right.