It is hard to explain because, well, I am a westerner. Yet I guess what we had is an evolved idea of the car show model. She looks beautiful and highlights all the right features of the car, but at the end of the day we want to drive the car... she isn't the feature. So even when you have a sexy protagonist you don't want to see her "act sexy" because that is dumb, you want to see her be badass. Basically in many ways it is the bait and switch.
So what a lot of games do is what I originally called "She has boobs, get over it" which was my way of explaining how the Tomb Raider series (not the posters and cover art) handled Lara Croft. In that she had incredibly large breasts but the camera angles didn't really focus on them, she was never really defined by her sexiness, nor did she suffer from sexy wounds. You have a lot of games where the women are wearing incredibly scant clothing but as far as the game is concerned "Who cares?". The games usually don't draw attention to it except to make a joke. Even in the cover art while usually... revealing... there is usually some sense of power or competence.
In fact western games that do have present sexy women to ogle tend to be comedies OR are comical characters. Conkers Bad Furday, Dungeon Keeper 2, Duke Nukem, and heck Milena while not in a comedic game was clearly not someone you were meant to take seriously. Excessive sexuality is usually something you are not meant to take seriously... OR is meant to be something to make you drop your guard (The Dark Mistress from Dungeon Keeper are one of the strongest creatures in the game. In spite being latex wearing dominatrixes). Even the Latex wearing nuns from Hitman were meant to be "Deadly clowns", the creators just weren't able to pull it off.
That is my best attempt to explain it.
In fact it is probably one of the largest differences between Western and Japanese games...
A woman you are supposed to ogle at... tends to be a joke in the west but is a serious character in Japan. Their outright objectification isn't considered a detriment to the Japanese while in the west outright overt objectification tends to be looked upon unfavorably on the character...
Unfortunately this also means that "Prostitute" characters get no respect in Western games for the most part (Remember. Outright "Objectified" women are not to be taken seriously) as well. While Japan tends to avoid prostitutes. Sure there are exceptions (Heavy Rain is a HUGE one... Damn!) but for the most part yeah...
Now there is also a difference between being the active sexual object versus the passive one and how subtle you are.
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There is a reason why I think the Old Lara Croft is better than the new one... even with her old looks... Mostly has to do with the fact that Old Lara Croft was considered unequivocatively awesome while the new one cries her way through her game because "She is a woman and thusely must PROVE she is awesome" the new modern day garbage I hate...
You know as horrible and sexist as the old videogame designs are... I'd take them any day over the new modern day garbage of women needing to prove themselves. I'll take 20 chainmail bikini women who kick butt, take names, and are in charge of their lives over one female character who cries, and sobs, and gets hurt, and must prove she can make it in a man's world.
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Though I am going to disambiguate to exclude those webgames... They are clearly a subculture altogether and frankly... everyone knows they are horrible.