The fees for Stripe are 5% + $0.30.
However when you take a deeper look you see that things are not so simple. Compared to PayPal's free product, you are not forced to leave your website and go to a 3rd party site to complete the transaction. Compared to PayPal's Web Payments Pro product, you don't have the $30 monthly fee.
Also this doesn't even taken into consideration the complexity and cost of implementing PayPal's Payments Pro api vs Stripe's simpler JSON api.
I understand this is a usability win, but doesn't this subject the original web app to PCI compliance rules?
If the form that the user puts their credit card info into POSTs to your web server, then you are on the hook. Now that I think about it, the form may POST to a third party payment processing web service from your web app which prevents the user from feeling like they have left your web app. In that case, I think that your web app is off the hook for PCI compliance.
Moving to other countries will take time as each country has their own banking/financial/etc issues that need to be dealt with.
It took years for PayPal's Web Payments Pro to go from US only to US, UK. And then a few more years to go to US, UK and Canada.
Amazon FPS has been around for ages and is still US only.
So it may be a while.