It might not be reasonable, but there is an explanation. It's been a while since I heared the podcast but Planet Money explained something along the lines that all the American banks are invested in an old, inefficient system of processing these transfers and there is no incentive to change. Here's the episode: http://www.npr.org/blogs/money/2013/10/04/229224964/episode-...

In Europe, the EU recently established the rule that all money transfers within the entire EU must be concluded within one business day. Thus most Europeans are surprised when they hear that it takes so much longer in the US.

EDIT: Another commenter pointed out that the EU directive is actually still somewhere within the legislative process. My misconception arose from the fact that I can't remember the last bank transfer that took longer than one business day.