Why write a heavy business plan that nobody reads?

Many of my start-up clients that go into a fund raising round want to develop a "heavy" (i.e., many pages) business plan in reality is nothing more than expanding a 30-page PowerPoint presentation into 100 pages of full text. "The potential investor asked for it". A waste of time.

• People don't read it
• It takes a lot of time and money to write it
• It takes a loft of time and money to update it
• Nobody updates it

I prefer maintaining and updating a good PowerPoint presentation with a special appendix (not to be presented on a big screen) that provides more detail on financials, workplans, etc.