It is unusual that Key to Time was released first in America; most of the DVDs are released first in Great Britain.
It was all to do with marketing. Apparently it was decided that American shoppers would prefer box set releases, and so the decision was taken (I think) to release Key to Time on Region 1 as it would fair better in the sales (not sure if it has or not)
Nevertheless it's superb news that it's getting a release over here in the UK, and is brilliant addition to the bumper stock of releases we're seeing this year:
The Keeper of Traken (Jan)
Logopolis (Jan)
Castrovalva (Jan)
Survival (Apr)
Robot (June 4th)
Timelash (July 9th)
Timeflight (August 6th)
Arc of Infinity (August 6th)
The Time Warrior (September 3rd)
The Ribos Operation (September 24th)
The Pirate Planet (September 24th)
The Stones of Blood (September 24th)
The Androids of Tara (September 24th)
The Power of Kroll (September 24th)
The Armageddon Factor (September 24th)
And with presumably a few more before the year is out