Every country is different, and I don't believe there is a correlation between theft and the degree of development in a country. Culture is more important, IMO. I didn't have any problems at all in Laos, Thailand, or Malaysia. I haven't been to Vietnam but I've heard a few non-bicycle-related theft stories in that country. My sense, however, is that petty theft problems are much greater in several European countries (e.g. urban Spain) than in southeast Asia.