Why they don't use XMLHttpRequest instead?

All tagging based analytics.

[fischermx]

I just wondering why they don't use XMLHttpRequest instead of those new Image(1,1) thing that they do?
Is it just to cover the very, very old browsers?
Or is there another thing am I missing?

[daveVk]

Reason one: XMLHttpRequest does not work cross domain

[fischermx]

Oh, god, that's why it worked in my localhost :(

Thanks for clarifying that.