I'm just wondering generally whether it is viable to run, say a blog, targeted to US audience from some other country and use paypal or other online services when dealing with advertisers and other corporate connections - basically acting as if it were a valid US business running the business. I currently don't see why this can't happen, and if yes, why don't we see more startups from around the world targeting US audience first online?
There is no legal (unless local laws of that country prevent it and vice versa) or practical reason (assuming your site is hosted on the internet) for you not to be able to run website aimed primarily at US audiences in another country and it happens all the time, indeed often at the cost of local markets.
It does however make sense to target a market you know and their are a couple of complications to targeting foreign markets, the US is a large market but sometimes its good to be the big fish in a small pond, then just another fish in the ocean.
Likewise there are many US companies target foreign audiences.
A few potential complications, international banking can be "fun" so if you are looking at doing larger contracts with advertisers then you should ask your bank to provide you with suitable banking credentials SWIFT and IBAN numbers for example.
In addition when dealing with international companies and cross border transactions working out where sales tax is applicable can be interesting depending on the scenario having no assets in the country you are targeting can be a good thing, and that could include hosting.
These and others are all however small complications and many sites manage to crack the US market.