It looks like they have a "North-South" divide too....
Why are Northen states more conservative than southern ?
Are they wealthier, is it the influence of the United States, or is it an ethnic thing (being less indian) ?
On average they arew indeed wealthier (though both the Mexico City and the state of Campeche, among the wealthiest in the country, voted Lopez - Campeche barely so). Mostly, this is the absolute lack of organization of PRD anywhere in the north - northern PRI hadn't split until now, so the PRD didn't have a foothold. Since they never had any governors, mayors, congressmen, etc. in the region, motivating and getting out their vote is hard. And the North is the birthplace of PAN - their first triumphs where in Chihuahua and Baja California.
An interesting feature is that a lot of the states that went Lopez did so by small margins. This is very much the case with Campeche, which still might switch in the final count. But also in Veracruz, Quintana Roo, Michoacan and, to some extent, Morelos (where PAN seems to actually have managed to keep the governor's office on the same day, despite attrocious scandals in the previous Panista administration) and Tlaxcala (where PAN actually governs). Even the PRD-governed northern states of Zacatecas and Baja California Sur (the two poorest states in the North), though won by Lopez, gave surprisingly good tallies to Calderon.
A big surprise is that Calderon actually won in Puebla. This is a PRI stronghold, but the local Priista governor Marin is embroiled in horrid corruption scandals, so Priista fall was predictable. But the patriarch of the local and national PRI, Sen. Manuel Bartlett, has called on priistas to vote for Lopez, and if there was one area where this should have worked is there. PAN never had a foothold in that state, and Calderon's performance is almost shockingly good.