Deflectors are only needed if you have a beam pattern that goes up towards the left. The HID headlamps on the IS have an almost flat beam (there is a tiny step up towards the left), but nothing like the 15 degree up-slope of "old-style" UK headlights.
This type of flat beam pattern is very unlikely to dazzle oncoming drivers and does not need beam deflectors.
If you look at the MOT tester instructions you can see the different beam patterns. http://www.motuk.co.uk/manual_180.htm
The traditional british pattern is type E, whereas the HID headlamps have the British American pattern (bottom pattern on the page, with a small step but no "kick up").