In Japan, you won't have to undergo any such hassles from hotels. Not even in the North. As far as China goes, I'd like to say a few things for your future referrence.
I'll bet my head that the hotels you questioned you were not the 5 stars, but the "business class" hotels (somewhere between luxury and budget). In most 5 stars, I don't think this should be an issue.
But, if your budget forces you to stay in a business class hotel, you'd do well to ask your cabbie who runs the Hotel. If it's run by a powerful politician, you won't be hassled. Japan, being a rich country already, along with a much more transparent law mechanism, doesn't have this problem.
This unnecessary hassle is done in the name of combatting prostitution. In a ultra fast developing economy like China, which is increasing liberalisation (i.e. more cash, more opportunities), everybody is looking to make a quick buck. This includes the law enforcement too.
Unlike in the past, where everything was based on seniority, today- promotion, perks in the law enforcement is related to the cases they register- thereby indirectly increasing the probability and frequency of hotel raids.
If a hotel you're staying at is run by a party boss, it will naturally get immune from such raids. You and you're partner seem to have lived together for a while- and the last thing you want is a BS hassle- especially after you've dished out your hard earned dough to earn that vacation of yours!