I wouldn't say all Japanese women are willing to look the other way like that.
The younger girls really do ask questions and are more willing to snoop around to
find dirty information on you.
But, yes, as you mentioned, many women are too oblivious to figure it out or
already know that Japanese men cheat on the side so they don't care about it.
What is nice about Japan is that a LOT of young girls and mature women are willing
to trade sex for money. Unbelievable the amount of hot models (former and active) that
go into porn or work at brothels. (Tanaka Hitomi, Handa Sasa, Aoki Rin, etc.)
Most recently, Takahashi Shoko has made the porn jump.
http://www.dmm.co.jp/digital/videoa/-/detail/=/cid=tek00077/?i3_ref=list&i3_ord=1
With a cute face and hot body like that, she could make it as a gravure model (albeit with trade-offs).
Fortunately for us men, she did some hard core porn.