Nicknames in Poland

In Poland nicknames are very commonly used. To give some examples of nicknames: Katarzyna is Kasia, Alexandra is Ola, Jakub is Kuba, Joanna is Asia, Tomasz is Tomek and so on. It is much more rare to hear the official name than the nickname. Seems also that in Poland there are also much less variety in names than in Finland. For example when I look at the list of the women working in human resources in our company half of them are having the same name.