I think Arsenal's mental strength has been great this season and is probably the biggest difference from last year. Closed an 11 point gap when everybody wrote them off, then another 8(?) point gap, added to that are the many last gasp winning goals and wins in the face of possible adversity (Ramsey leg break, 10 men on Saturday, coming from behind a few times etc.)
They look more together as a group, I don't know if Adebayor and Toure were the negative influences but an improvement has been made in that respect