Been to Vietnam several times and Cambodia once, never had go pay anyone off or felt remotely threatened. Actually felt safer than some parts of China.
When was the last time you flew out of the country?
I agree with you as I have knowledge about these too.
The officers deployed at entry points of all countries where corruption exists have responsibilities and are afraid of being caught in unpleasant situations, especially issues connected with complaints over demands for money.
The reason is that these officers are afraid that if someone make a complaint against them for their "unreasonable demands", there is bound to be some sort of internal investigation conducted by their departmental head. This will expose these officers to unneccessary queries and may result in them being transferred out to other remote provinces or areas in their large country.
If such a thing happen they will loose the "fringe benefits" that they enjoy at airports, etc.. These "fringe benefits" can be in the form of passive income or gifts gotten from businessmen who use the airport dailly to bring in or take out certain types of goods that may be taxable or prohibited, respectively. More often then not, these businessmen would offer money or gifts on a monthly or "as and when basis" to the customs, police or some other officials so as to be able to get away without hassles.
That is why officers at such entry points do not trouble tourists, as to "cross the boundaries" may put them in difficult positions and in danger of loosing their comfortable positions.
I got this input from a Customs Officer friend attached to the Provincial capital of a 3rd World country. He makes more then enough from such "illicit" deals and will never ever want to get into any form of trouble that may be disadvantageous to him and his "survival"
In Malaysia it is the same too. The officers attached to the land crossings will never want to be caught in unpleasant situations.
Why kill the goose that lay the golden egg?