Kavya,
when VO calls the managers, they know it that they might get 50% of affirmative answers. They too work under pressure where giving information about an employee is not the only thing a manager deals with. Neither the managers or the offices get paid for providing such information... I have heard numerous verification calls in India and a lot of the managers gave wrong or erroneous information or requested the VO to call back a lil bit later but in most occasions the VO's never called back again.
I guess VO's are just happy with the info that the employee works as " profession " and whether or not the reference letter was indeed provided by the manager with whom the VO's talking to.