I think that 99% of 'accidental' deaths in Hollywood are drug related (ie: overdose). The media just drags it out saying "could have been an accident" or "possible suicide" just to sensationalize the death of a 'star' and to get mroe ratings for their broadcast. What do people love to watch the most? The lives of the rich when they are at their lowest. And what better way to exploit the unfortunate death of someone in the public eye than to drag it out for as long as you can.
If you watch the more recent interviews of H Ledger, he was obviously on some kind of stimulant whether it be coke (more than likely) or speed or whatever.