Coverage IS a topic in Europe when it comes to international hotel chains and their loyalty programme.
I just now joined NH World, because a NH hotel was my choice when planning a 5-night-stay in Groningen, the Netherlands. Until today I never stayed in one of the NH hotels (only in Golden Tulip or Tulip Inn that thereafter changed to NH).
I thought it does not hurt to join their programme since I share the perceptions that their European coverage is quite good. I will report back on my stay.