Working on Vacation: what's the point?

Last week I got a phone call from a client who was on vacation. I couldn't understand why he would make a work call while on vacation.  Seems counterproductive.

I usually don't tell people how much vacation I get.
And it took me 32 years of working 50 weeks a year to get to this point.  But I take vacations like the Europeans do - - six weeks during the summer. 

I claim it makes me more productive the rest of the year. (photo of paper or white birch trees along the road near our cabin) How much vacation do you think people should have?