Remember that these are MINIMUM recommended, and other criteria in your design may take precedence.
For example, designs that must meet Underwriter's Laboratories (UL) approval greater spacing is required. Other factors such as humidity and pollution may also affect performance.
Wherever possible - within your design constraints - include extra clearance.
Two terms used in calculating appropriate distances between conductors are creepage and clearance, an introduction to these concepts can be downloaded from our FILES area.
An online Creepage/Clearance calculator based on IEC 60950 requirements can be found at http://creepage.com