Another factor might be that full QWERTY keyboards are more popular in US than in UK.
It is also interesting to see that US users are increasing their year-to-year numbers of browsing the mobile web and number of pageviews have increased with 89 % and 127 %. All the above numbers come from a recently released report from M:Metrics.
In Mobispine we also like when users have flat-rate data plans and nice phones with big screens ad keyboards, but never forget that the goal with mobispine is to create a really good user experience for average phones without nice data plans.
/ Joakim, Mobispine team