Their culture being the source of otaku subculture and other such related things doesn't mean they're any less able to be newfags taking a joke too seriously. Then again, those pictures *could* be jokes. But, I'm pretty sure waifusm like that does exist plenty in japan, so it doesnt matter if they in particular are.
Fun fact, 2ch has a word for 'winterfags' as well as one for 'summerfags' cause of how japanese schools do vacation time.
Of course, 'newfags taking a joke too seriously' is inept and mostly wrong. Im pretty sure(not entirely) 'mai waifu' was originally a meme from something or another, maybe azuma, but people doing it seriously doesn't mean they took the meme too seriously, and they wouldnt be acting like that if they didn't. That kinda fantasy romance and idolization of characters almost certainly existed beforehand. Fuck, the idea of people doing it with celebrities(maybe idols in japan?) has long been a well known meme.