I'll disagree here. I've been through several successful fund raising rounds, exclusively from corporate sources. Granted, this was not inner-circle silicon valley VC. But not a single deal would have happened had we not had a 20+ page business plan with detailed financial projections.
Of course your mileage may vary. The guy that just walked out of my office checking his blackberry for a $9 million wire transfer only had a single presentation deck and a business model.