With Germany being in the EU, you can also incorporate in whatever EU country you want. The UK is obviously out for now, but take Estonia for example. Makes taxes a lot more complex for the company, but much less so when compared to YCs way of transforming into a US Inc. with a German / EU local entity. Especially when there are now US based operations.
That being said, there is nothing wrong with sticking to one market. Not the last reason being to avoid the above mentioned entanglements.