Here's the full list of countries where PayPal is now supported: Austria, Belgium, Canada, Finland, France, Germany, Ireland, Italy, Netherlands, Spain, United States, United Kingdom. One important notice: "PayPal can't be used to purchase devices or accessories on Google Play or for other purchases that use Google Wallet outside of the Play Store."
Google has always tried to promote its own payment service, whether it was called Google Checkout or Google Wallet, so why would Google add support for a competing service? Google offers an answer: "Sales of apps and games on Google Play are up by more than 300 percent over the past year. And today, two-thirds of Google Play purchases happen outside of the United States, with international sales continuing to climb. We're hoping to fuel this momentum by making Google Play payments easier and more convenient for people around the world."
In addition to supporting PayPal, Google also added carrier billing to 7 more countries (including Singapore, Thailand and Taiwan) and Google Play gift cards to 13 more countries (including Japan and Germany). "Developers based in 13 new countries can now sell apps on Google Play (with new additions such as Indonesia, Malaysia and Turkey), bringing the total to 45 countries with support for local developers."