Flights to/from a hub are often more expensive than those exact flights when taken from another destination. I'm flying BOS-MSN this week (through ORD, of course). For the same dates and times BOS-ORD was about twice as expensive. Likewise for a couple of random dates in September:

BOS-GRU in C: $4555
IAD-GRU in C: $6260

So, lucky for the rest of us, it's not just MEX. Too bad for those who live in ORD or IAD!

Michael