It's predictable that every Stripe-related post will have non-Americans asking when Stripe is coming to their country.
Less common or nonexistent are the comments where someone posts a link to the beta Stripe clone they are building to launch in their country. Do it, at worst you'll be acquisition bait.
Most countries don't have the same facilities as the US for creating payment-related businesses (financing, engineers with expertise in the field, close to the backbone visa/mc/banks, bureaucracy). It's probably much easier for an established company to bully their way in, than for one to grow locally.
That said, there are no excuses for trying, and there are exceptions; I sure hope they succeed. I'd love to work in an area as disruptive as this.
This was more of a technical challenge, whereas, implementing international payments is beyond just technical and likely includes many legal hurdles and navigating many different policies. It has to be extremely difficult, otherwise, Stripe would have done it already.
The Stripe CEO was in Nairobi two days ago for a meetup at one of the startup incubators. This was the one question every dev had on their mind - the short answer, at least for those of us in Africa - is "don't hold your breath". I have to agree with runako on this one.
TL;DR The international interbank system was designed to move large lumps of money rather than a high speed trickle of micropayments. Additionally, fraud, already a big problem with online payments, is compounded by cross-border activity.