From their mail:
We are happy to inform you about the recent Tier upgrades .
If you have any suggestions or queries please mail us, we are happy you assist you anytime.
Tier A Australia, Canada, United Kingdom, United States
Tier B Italy, Switzerland, France, Netherlands, Ireland, Sweden, Spain, Belgium, Japan, Portugal, Spain
Tier C Poland, United Arab Emirates, Saudi Arabia, Egypt, Czech Republic, Indonesia, Thailand, Vietnam, India, Malaysia, Singapore, Brazil, Russian Federation, Mexico, Pakistan, Argentina, Bangladesh, Greece, Cyprus, Bosnia-Herzegovina, Colombia, Turkey
Tier D All other countries