In reply to TobyA:
It is indeed confusing. The standards seem to be:
CE EN1077 class A - for race helmets with a hard shell over the ears
CE EN1077 class B - for the type of ski helmet that 99% of helmet users wear
PCSR-001 - the new ski mountaineering standard.
Weight wise it's interesting looking at the lighter end of the spectrum for the standards:
CE EN1077 class A - 600 to 750g
CE EN1077 class B - 350 to 400g
PCSR-001 - 240g
If any of this makes for a safer fall than when wearing a hand knitted bobble hat remains to be seen but there are certainly differences in what's required for the standards.