A couple of years ago I obtained British citizenship, after living in there for approximately 10 years. As part of the application process I needed to document every day spent out of the country, over the proceeding five years.
This was not as simple as counting the stamps in my passport, and I didn't really know whether the Home Office had any other way of tracking me. It took several days for me to compile the complete list.
As an example, fly London to Belfast, rent a car and drive to the Republic of Ireland. No stamp in the passport.
A few times traveling to the European mainland, other than by air, resulted in a lack of either arrival or departure stamps.
My passport was never stamped on departure from the UK.
Now I have British citizenship, I regularly travel across multiple EU borders and no crossing is recorded in my passport.
My British passport, although two years old, does not have a single stamp in it, and I've been resident in a different EU country for the past year.
They do well with this when it comes to tax, I don't see why they wouldn't do well just because it's a question of citizenship.