can someone please explain...

What exactly is it that leads [married] men to use the services of a prostitute or hustler?

Senator Apologizes Again for Prostitution Link

Well, as far as married men and hustlers, I guess that would be pretty self-evident: the need for secrecy and discretion based on perceived unacceptance of their real orientation - gay or bi.

As far as married men with prostitutes, is there something lacking in their marriage? Is this part of the primal need for multiple partners to insure continuation of the species? Huge egos?

I think that I might tend to give more credence to the first possible explanation - something lacking in their marriage. If this is the case, these men certainly are cowards. They don't have the cajones to deal with the spouse they chose in order to confront their problems, sadly most of the time at the expense of children.

As far as their wives, where have they been? If there are problems, they are also part of the scenario. I think Senator Vitter's wife said the right thing in her reaction seven years ago regarding Hillary Clinton:

His [Vitter's] wife, Wendy, told Newhouse News Service in 2000 that if her husband cheated on her, she would react less like Hillary Clinton and more like the Manassas woman who cut off her sleeping husband's penis in 1993. "I'm a lot more like Lorena Bobbitt than Hillary," Wendy Vitter said. "If he does something like that, I'm walking away with one thing, and it's not alimony, trust me. I think fear is a very good motivating factor in a marriage." Washington Post

Now she has changed her story:

Mrs. Vitter, speaking briefly afterward, defended her husband, said that their marriage was “not perfect” but that “we choose to work together as a family” and criticized the news media for “following us every day last week.” New York Times

According to some sources, Vitter was frequenting prostitutes back in 2000 when she said she'd have more than his cajones. Exactly how long has she known about his indiscretions, if they've put it behind them?

Of course some men don't frequent prostitutes. Some are what might be called serial-husbands. In other words, multiple marriages after divorces or annulments. Helllllooooo, Mssrs. Gingrinch, Guiliani, et. al.

pseudo-prostitution?

just asking...