...uh...I think because they are an upgrade option in a few of EA's games "Need For Speed"
Or maybe even mentioned in the "Fast and Furious" series ;p
Honestly, The bi-xenon are standard here in the states on MK5 GTI's. I know that the oem ballast's are spendy.
The US cars went back to Halogen on the MK6 ;| And, back to xenon plus LED for the MK7.
I believe they are popular because they were the next "It Thing" added to performance models at one point. So perhaps for that reason they must be one step above the rest.