Sometimes I also don't understand when I say thank you and the person I thanked for (westerners) said "thank you" back at me or "no worries" or "no problem", why not "you're welcome". I might also have 'value standard' of expecting "you're welcome" like some of you would expect "sama-sama". But apparently there are other ways to say/express it. Maybe that's part of the culture or just habit of one person. Why bother.
However, I hope this discussion is not leading to stereotyping about a certain culture or race. It's been spread widely to say 3 magical words; Terimakasih, Maaf, Tolong (Thank you, Sorry, Please) all over the world, not just in Indonesia, shows that it's not an issue of a specific culture or country. Therefore, I wouldn't agree to highlight a broad aspect such as culture as generalisation of a few people's specific behaviours.
In fact, it leads me to a question, what is your wife's intention when giving/helping? Is it purely altruistic gesture or does she expect something in return such as saying "thank you" or other appreciation to fulfil her value standard or your standard of good manner.
Sometimes the way we criticise one's behaviour only show more about ourselves than them. There's a saying, when you pointing one finger to somebody, at the same time three fingers pointing at yourself. But what do I know, I'm just psychobabbling.