Pedikůra, manikůra

I keep seeing the spellings above in Czech, even though officially they should be pedikúra and manikúra because the ů, which appears in the middle of words, shouldn't be used in words of foreign origin. Nevertheless, I wonder: if you can write pedikúra and manikúra, how come it's wrong to write struktúra (structure) and agentúra (agency), even though these two words can, and sometimes are, pronounced with a long u. Is it maybe that they end in tura whereas pedikúra and manikúra don't?