You can also take them one day after.They are highly effective in one single dose.
Actually most pill pamphlets come with the warning of the exact opposite. The reason she probably didn't get pregnant that time was a fluke. Unless you're thinking of 'the morning after' pill which has a higher concentration of hormones to discourage the egg from attaching and gets the uterus to shed its lining.
As for all the side effects, yes they can cause cancer and blood clots. In a study of 1000 women if only one women develops side effects they have to include a warning. I don't have the statistics, but they are out there is you care enough to look.
The cost of pills depends on what pill your doctor puts you on and if there is a generic version. Some women also don't respond to some pills and have side effects (mood swings, nausea, on other conflicting meds etc)
Women can be put on the pill for other reasons besides contraception. PCOS (polycystic ovarian syndrome) causes wildly irregular periods and other symptoms which going on the pill can alleviate. Extremely bad acne is another reason.
As for Polish girls not taking the pill: It is just like any other women located anywhere. Some women are crazy and want your baby (this happens all the time in America), some can't be on the pill for health reasons, and maybe others haven't sought out the information and have only asked the wrong people and have been misinformed as to the benefits and downsides to taking the birth control pill.