They are measuring total compensation. In European countries, you have five weeks of paid vacation and money that is put into your retirement fund in addition to your salary. Plus sick days. That is worth 10-24 % more than your base monthly salary.
Where are you pulling the five weeks figure from? It's more like 20ish days, after that if your employer is ok with it you can "borrow" vacation and pay it back by not generating more vacation days while you work or pay when you quit your job.
Retirement funds, I don't know about the rest of EU, but in my country are basically a scam - here you are forced to pay 10% of your gross salary per month into the fund and you can start getting pension after 35yrs of work (provided you are older than 70yo), that means I'm paying money I will NEVER get back, since median age is going up and employement down, no one will be around to pay my pension like I'm paying my parents' with my salary.
Sick days are on the company only for the first 3 days, after that the healthcare system pays you (80% of your rate, iirc)
IT, you get 100% for the first three days covered by the company, 50% from the 4th day till the 20th and 66,66% from the 21st to the 180th day covered by healthcare - incidentally 180 days is the maximum number you can be on sick leave in a year
The spread of US developer salaries appear to be insanely high though. Median is "only" 70k according to this site: https://www.payscale.com/research/US/Job=Software_Developer/...