Some of the great keepers in England's history have played for struggling sides.
I generally tend not to judge keepers on number of great saves, but instead on the least amount of foul-ups, for two reasons. Firstly, as a defender, I'd far rather be playing in front of a guy who may not pull out the brilliant saves, but who can be relied upon. And secondly - and this is the main reason - quite a lot of what the media hypes as "great save" really isn't. With notable exceptions (Banks v Brazil, Schmeichel v Vienna, Seaman v Sheffield Utd, and so on) they're mostly saves where, had the keeper not made them, he would have been pilloried by the media. Thus they're regulation saves that the keeper has either dealt with as he would be expected to, or they're regulation saves that some over-hyped keeper such as Casillas or Buffon has made look better than it really is.
As a result of my general outlook on keepers, the fact that Foster made only one bollock (that I can remember) despite having had more oppotunities to **** it up than everyone else is impressive, to me.
I don't expect to have changed your opinion of him as a result of this post particularly, but this is my reasoning.