50 pages – Ouch! I feel your pain. The really scary thing is that this sort of stuff still seems to be happening despite this being an really old problem.

What you’re describing sounds like what software engineers would call a “Waterfall model” which kind of assumes that if the specification is thorough enough then it will miraculously describe exactly what’s needed and that the programmers will miraculously implement every requirement to the letter.
In theory software engineering has moved onto more hip and trendy “Agile methods” which try and keep specifications small and development iterative but the situation that Mike is describing is all too common.
My contribution to the issue is called “Writing a creative brief for a computer exhibit“. But perhaps a better way of summing it up would be to say “A specification is not a special tool whereby anything you write will magically happen – its a method of communication to tell people what you’d like them to do”