Different ranking on Google+ccTLD for same keywords

Which factors are considered here?

[fischermx]

Some time ago I started to rank number #1 in google.com, for my main keywords on one of my sites.
I was happy until I notice that in google.com.mx, I'm #2. In google.com.co I'm #4.
In google.com.ve I'm #6.
In google.com.ar I'm #3.

And on and on. Different results for same keywords in different Google+ccTLD.
Are they just datacenter differences? I mean, are this searches being responded by different datacenters, or does Google really want to set a difference in your keywords popularity according to the country you're supposed to be on?