Public Transport Eh?

I work from home, but my wife has just started back at work in the city, which means a drive and two buses; a drive, a bus and a train; or just driving all the way.  At the moment, as in the past, she is using one of the public transport options but today's experience may be enough to put her off for good.

I will spare you the details, but lets just say the bus broke down on the motorway, the replacement bus didn't stop in time, the replacement replacement bus was going to the wrong place and... ok, you get the picture.  

It got me thinking about the last time I broke down on the motorway in a car.  It was when I was a student and I was driving a rusty old 1970 Holden Kingswood.  Cars now are reliable.  They rarely break down and are vastly improved on my set of student wheels.  One the other hand, I quite frequently see a broken down bus on the side of the road, with the familiar heavy duty tow truck in attendance.  Given that they make up only a small proportion of vehicles this would be somewhat of a concern.  Why is this?  The buses themselves seem relatively new.  Is it that much harder to make a bus reliable, compared with, say, a modern truck?