I can’t tell you for sure why Durian has such a different affect on people exactly, but there is something else that smells bad to some people and not to others and I would guess its for the same reason.
When some people eat asparagus, their pee smells really horrible for the next day or so. Other people can eat asparagus and they do not report have horrible smelling pee (you can test this yourself if you eat some). For a long time it was thought that the reason for this was that people had different versions of an enzyme that produced (or didin’t produce) the nasty smelling chemical in their urine. But more recently it was found the majority of people did infact produce the chemical and the difference was not production, but perception. Some people could smell it and think it smells bad, and some people can’t really smell it and therefore don’t really mind (You *could* test this yourself if you and your class don’t mind smelling each other’s pee, I wouldn’t advise it though!)
Recently it was found that a tiny change in DNA near the gene for a smell receptor is associated with the ability to smell asparagus pee. Because I work at a gene sequencing institute I tested myself for this change: I do have it and I can confirm that I do smell the asparagus in pee.
So it turns out that we all have different versions of genes for smelling stuff, and depending on what version we have, we smell things differently or not at all. There are a few other known examples of this, but there is a lot more to find (there are hundreds of different smell receptors, after all). So to get back to your question, I bet the people who like the smell of Durian fruit probably have different smell receptors to those who think its disgusting.
Since I come from a region that likes to eat durian, here are my two cents’ worth of contribution to the discussion. Personally, I don’t find the smell of durian all that offensive (of course, it is a different story when it is in an enclosed space. In fact, in Singapore, durians are not allowed on the public transport). In fact, I enjoy the occasional durian when it is in season. It may be possible that different people may perceive the smell differently due to smell receptors as Darren suggested. Another reason I can think of is because of culture. Food and cultural identity are closely related. Eating and liking a certain food is sometimes a part of national and cultural identity. Having grown up in an environment where durians are common, I may find the strong odour more acceptable simply because I have been exposed to it since young. Likewise, I find the smell of some cheeses offensive because we don’t eat that much cheese here. This is probably the same reason why some food from other parts of the world can seem “strange”.
There are other things that smell different to different people too. I used to live in Vancouver, Canada and thought it was really strange that lots of people seemed to burn their toast. As we walked around, I could smell lots of burned toast. Eventually someone told me that it was the smell of skunks, and that no one else thought it smelled like burned toast, they all thought it smelled terrible!