There's the argument of course that Ledley wouldn't have stayed at Tottenham if he'd been fully fit and therefore the best English centre half around.
I think Benjamin's point stands unfortunately, the players who are good enough to play champs league regularly and fight for titles, aren't going to want to stay here long term. But we've been lucky enough to see so many amazing players and although they tend to leave due to the quality of the team around them, the ratio has been changing in the right direction for ages now.
It helps there not being a solidified top four any more, means players like that can believe in us a bit more