You have it partly right. They are in fact rarer amongst certain
collectors. To someone who doesn't speak Russian, or have contacts in Russia, or fly within Russia, they probably will be rarer.
The one thing which irks me with collecting these cards, is some people will try to claim that a card they are offering is "especially rare". A prime example, was a An-24 Uzbekistan Airways card. The price this person was asking was equivalent to a month's wages for the average Uzbek citizen. After trying to explain to this person that this card was not all that rare, and him not buying my reasoning (with some extra commentary from him as to why it was so rare [it sounded like it came from Mars]), I contacted my mate in Tashkent, and he got me the whole Uzbekistan Airways fleet (except for the Yak-40 which is coming soon).
As to why I collect them....because that is where my passion in aviation is. Much the same as why the person who started this thread collect British Airways card.
I have only been collecting safetycards for all of 3 months, and already have some beaut cards in my collection; with a lot more coming in the not too distant future.