Sales in some countries are extremely poor for products that can be pirated. To give you an example, read a report recently that 90% of software in countries like Spain and Italy are pirate (latest version of Microsoft software sold openly on the streets for a few Euros) so you have to be careful if trying to sell software to such countries.
Well - obviously someone else has to care about conversions - otherwise you will have no ads showing - and if you bid 5 cents to show in Nigeria, for example - you just might be the only bidder for that geographic region.
Your question cannot really be answered because if you have a site about, say - big ticket consumer electronics - you won't get US based companies (with US level prices) bidding on their terms in countries where shipping might cost the same as the product itself.