I happened to be in Mexico for Cinqo de Mayo a few years ago. When in the SCUBA shop getting all set up, we asked where all the big parties were going to be for that, and the gal working there said "we don't celebrate that." When I told her it was a big deal in the USA she just frowned and said "that's strange."
Cinco de Mayo is mostly a holiday fiesta mostly created by Jose Cuervo and Corona. The battle of Mexico's triumph over the French at Puebla just isn't that big of a deal south of the border.
This isn't true - this is like claiming Valentine's Day was created by Hallmark. Cinco de Mayo isn't celebrated much (not exclusively) south of ther border but it is a big deal north of the border as a way for mexicans and mexican-americans to embrace and celebrate their identity as a people. Just because the gringos have turned it into a marketing consumeristic drunkfest doesn't mean it lacks vitality to the people who understand where it comes from.
Plus, the experience of St Patrick's day and Cinco De Mayo show that no matter where a person comes from, everyone loves drinking and that is something that brings us all together.