Chavez's 2000 and 2006 challengers were from Zulia. Capriles isn't.
There's that factor, but Zulia is/was an opposition stronghold at other levels: legislative (2010), referendums (2007 and 2009).
Remind me... are the low margins in the far south part of the historical pattern?
If you mean the Chavista margins in Amazonas, no, that's actually another interesting thing which appeared in 2010. Amazonas used to be one of the strongest Chavista states, but the PSUV did poorly there in 2010 (the PPT won 41%) and it seems like Chavez did poorly there again this year.