Checked the censuses:
USSR:
170,467,186 (1939)
208,826,650 (1959)
132,164,569 (1940)
179,323,175 (1960)
USA: +47 mln
I'd say it's pretty comparable, if you also consider that 26 mln Soviets were killed in WW2
A better comparison is Russia by itself:
1939: 108,377,000
1959: 117,534,000 (+10% over 20 years)
You have seen that in stats or just assume? Because civilian causalities in WWII outnumber military ones. Old people, kids and sick people are extremely vulnerable during wars and die a lot.
Especially in WWII. First, obviously holocaust - most victims were from Eastern Europe and old, sick, kids had even lower chance to survive then physically strong people (not that it was high there, but). Second, German army was cleansing Eastern Europe for German settlement. That meant whole villages routinely burned out to ground. Third, famines and such, cause military extracts resources from people.
BTW: WW2 losses are still exorbitant, even if we subtract those 10 millions, but no longer that "impressive" (Poland lost 6 millions people, which was almost 20% of the population, killed by Germans and Russians - till 1941 Hitler and Stalin were best pals).
Ukraine's Holodomor happened in 1932-1933, and the census I mentioned is from 1939-1959. If you are implying that they were hiding Ukrainian losses in the 1930's and secretly added it to WW2 kill count then it's not quite true, censuses in 1926 and 1937 registered a drop in Ukrainian population from 31 mln to 26 mln. The results of the 1937 census were declassified only in 1990 and the revised number (26 mln) was estimated in the 1990's after the collapse of USSR and on the basis of declassified documents in Soviet archives.
>adding to the WW2 kills victims of Soviet Gulag system (about 2 millions)
Documents from the Soviet archives number the total deaths of prisoners in the Gulag from 1941 to 1945 at 621,637 (Evdokimov, 1995)