The media sucks there is your answer (ha ha ha). I think people moralize and sympathize with Philip Seymour Hoffmann's death more because he died a broken, sad man. He let life get the best of it, and lost to life. It’s sad because we can all relate to this, and it’s tough to see a fellow man lose to the harsh realities of life. Philip can be us, we can all end up just like him. So we pity him when deep down we are all scared. As oppose to the race-car driver and Paul Walker. Most people don't choose to something as openly reckless as speed racing and driving (doing drugs is reckless too, but its a different, more personal type of recklessness). We look at them as being fools who tempted life and die as a result of their naivety and "stupidity." Taking drugs is stupid too, especially the more serious kinds, but we empathize with Philip in a personal and impersonal way (yes both). Its also way easier to relate to Philip then Roger Rodas and Paul Walker because most people don’t willingly, openly and boldly put their life in danger.
In relation to media they understand this and use it to their advantage to promote their own agendas. They love to play the devil’s advocate, but they switch roles so easily and swiftly. The media also loves to play all sides, and when they are called out on it, they retreat, take no responsibility and play the blame game to divert attention from them. The media also loves to undermine and deceive people. In this case the agenda is speed racing is bad, and don't get out of line, while drugs are bad, but its ok because we can use and capitalized your death, as an example that drugs are soo bad. Its weird but its seems like the media seems to display the message that dying from a drug overdose is cooler and more acceptable way to die.
Even so, three men are dead. Dead and leaving behind families, children, "fans" and admirers. People that love and care about them. It's unfair about how the media chooses who died "better" who died "good" and who died more "acceptable-ly (i know they are not words lol). Even so, life is not fair and it isn't supposed to be fair.
btw lee lee your answer is interesting ... the speed racers died doing what they love while Philip died doing something he had to hide and was ashamed off (until the end) maybe the media is also giving us the message that death is this really bad scary thing that we should all be afraid of and that best/acceptable death is a death that is deserved cuss death is bad. hmm..