A very US-centric perspective. Whereas the folks in Europe do it in 3-4 years, come to the US and do a 2-3 year postdoc (with higher pay than a PhD student), and are ahead of their American peers.

Also, depending on where you do it in Europe, the pay as a PhD student is higher. At the extreme end, I knew students getting paid $60K/year in one country, while I was getting $24K/year in the US.