Editing WoW:API random (section)

=== Notes ===

The range [0,1) of math.random is exclusive, meaning that you can '''never''' get 1.0 exactly. Note that the returned number is not an integer, except the special (very rare) case of 0.

The other ranges of the functions are inclusive, and will always return integers.

It should be noted that the reason math.random does not allow 1.0 to be returned has to do with code they implemented to avoid issues on SunOS systems. However, they "correct" this issue by using modulus division. This has a side-effect for all non-SunOS systems making 0.0 twice as likely to occur than any other randomly generated number. In other words, when it would normally roll a 1.0, Lua changes that to 0.0 - so both 0.0 and 1.0 return as 0.0.

It has been suggested that the game client might seed the RNG when it is started

Source: http://forums.worldofwarcraft.com/thread.html?topicId=15443405133&sid=1&pageNo=10