... On cars (and bikes) they are only legal if they have automatic self levelling built in...
I thought this was the case too, but can't find it in any UK or EU legislation. All there seems to be is the MOT requirement that where self-levelling equipment is fitted, it has to work. Presumably vehicle manufacturers have to include that if HIDs are the OEM fitment, but I haven't found anything stating that HIDs can't be retrofitted to vehicles without self-levelling kit.
Even if that's not the situation, the law has failed to keep up with developments in lighting.
Self-levelling is only a partial solution to the problem of dazzle… it can work some of the time (though to work on bikes it has to do more than take care of pitch, bikes bank to go round corners so it needs to compensate for movement in the roll axis too), but even the best set-up system is bound to get caught out in some conditions and the answer is not to throw ever more technology at the problem but a sane limit to the quantity of light.
The old wattage limit worked when incandescent bulbs were all that was available, the huge increase in efficiency that discharge lamps offer has sidestepped that legislation and it should be replaced with something based on lumens (total quantity) and candelas (intensity, which would also affect cyclists with those bastard bright LEDs).