Successful .coms that taget the US but are not actually in the US
 

Excluding poker and porn, of course.

Can you think of websites targeted at the US general population that do well and whose parent company is outside of the US?

Knowing the culture and slang will bring you some extra's but it's better to have reps or people working in the USA to maximize stuff as good as you can if you're not from the USA.

This is no problem at all for us.

However, our concern is that since this is not an adult project, it will probably get some curious people wanting to know who's behind it and they might feel a bit disappointed that we're not in the US.

I am Dutch and people from around the world have bought from me for 21 years.
Focus on your service, quality and reliability more then the rest untill you can open an office in the US and hire local people there if the project is rewarding enough for you.

A few of the large forex, debt consolidation, and finance sites are based in the UK or Europe. These sites target American markets, and based on the average CPC rate of these niches' keywords, they are quite lucrative.

One example of a non-US .com company used by a lot of US people is Skype -- although they were acquired by Ebay, they gained their popularity among US users as an independent European company.

Aren't most online marketers targeting US audience? That includes everything from tshirts to electronics...

It is complicated to explain without giving away the idea. Maybe next year, when I finish developing it, I'll let you know if it worked or not :P

Not sure what to say