I've noticed that there now seems to be a need to classify and categorize Muay into either Dutch/Euro or Thai style, particularly by our American brothers who until very recently haven't had as much exposure to Muay Thai as Europe.
It reminds me a bit of the early UFC's where everyone was required to fight under the distinct banner of a system/style.
I definitely concur with Khun Kao in that the differences in Muay between Westerners and Thais is a result of training methods and culture.
It's almost impossible to realistically replicate full Thai style training outside of SE Asia. That is, being brought up training full time, twice a day with a dedicated trainer, surrounded by like-minded professional fighters fighting for an income for their families. This method of training without question produces very capable fighters to say the least.
In an attempt to compete with Thai fighters, Westerners have had to be more scientific in their approach to training, having fewer but intense training sessions. Better diet and nutrition, use of modern gym equipment, superior health and medical care...and cooler weather!!! We've learned to effectively use combination striking to try and counter the naturally instinctive style of the Thais.
Even Thai instructors teaching outside of Thailand have had to modify their teaching and training methods to cater to the western lifestyle/culture.
I do believe that with more and more westerners training and fighting in Thailand that training methods, skills and perhaps styles will be closer to being on par with the Thais. For example, you can see these days that there are a lot of British camps training in Thailand regularly, absorbing a lot of the Thai fight culture and methods. They don't seem to have the need to label themselves as a Euro/Dutch/Brit school, merely as a Muay Thai camp. No doubt they adapt their methods to the Brit lifstyle/culture.
I don't believe it's really as simple as lumping a style into a single specific category. Ultimately, it all falls under the Muay Thai umbrella but almost all westerners have to learn Muay Thai in a manner which is different to a Thai fighters'. So I'm really not sure if a person can truly identify a "style" learned outside of Thailand as being Dutch style, or French, British, Japanese etc. To me, it's foreign or Thai because all foreigners train similarly compared to the Thai way and styles vary from school to school and individual to individual.