I think a major factor in samsung's success is its hold over the developing countries, low end devices and microsd card. In my country I have seen only 5 iphones (i live in a city though) physically and it's not unusual as they cost like $800+ equivalent at launch, without the desired features like expandable storage, ability to share whatever file you want with any other device, different screen sizes, and really really low price.
Carriers don't exist in my country and that makes things far more in favour of someone like Samsung.
Cloud is meaningless with low income levels, high data charges and crappy coverage; so microsd is killer.
Everyone (I am not exaggerating) uses pirated music and other stuff and thus itunes doesn't mean jack.
Well, my points are probably more towards what makes android successful. But particularly for Samsung, I think the marketing thing does work really well. I have seen in almost every reputable retailer who also deal in other brands have a dedicated samsung employee to give demonstration of their phones while for sony or LG, even the exclusive showrooms had the real phones in boxes and only plastic demos were on the table. So anyone who goes to a store to buy a phone ends up getting a samsung midrange phone like galaxy duos or grand.
And yes, that's how people here go to a store, not to buy an iphone or a galaxy phone or an experia, but a phone. So they make decision in 15 to 30 minutes balancing between price, size, specs, camera and look and get a samsung phone because that nice lady showed them what and how they can do things in the device, while other brands are still in the shelves without human contact.