I'm in the UK and I've spent about $600 on directory submission over the past few weeks
I think the exchange rate has a lot to do with it - it was $1=£0.50 a few days ago. Because my e-commerce sites earn in £'s, I can afford to spend a lot more on directories in $'s.
Even UK sites that earn through adsense have a higher earning potential because of the exchange rate.
Another factor is that I don't really come across any UK directories, mainly because most webmaster sites/forums are US based.
I guess theres a gap in the market for UK directories, especially business/shopping directories.