Because both are struggling to get into what is an improving team. Only worth signing Defoe if he is £8m or less. Huddlestone is injury and suspension prone and is about as quick as Adam. If we signed them we would only be funding Spurs to get better whilst standing still ourselves. Never trust anything involving Harry. Defoe would be us replacing Kuyt or Bellamy, no more than that really. If we were serious about such a move someone like Defoe would still be behind, Suarez, Carroll, A.N. Other striker.
Given that Defoe is an out and out goalscorer I find it hard to believe he'd be below Carroll in the pecking order - who in the last few games particularly has been lamentable and has looked as likely to score as Pepe Reina
I'd say for £10m it's worth a punt but i agree with your reservations about Huddlestone - he's too hit and miss, injury prone and his inability to get a look in this season must say something