To maybe expand on my question, I'm fairly familiar with the transition from the late Middle Ages to the early Renaissance in England as far as the push from the noble/burger classes against the power of the king (the Magna Carta et al.) -- and that this type of struggle didn't take place in France until the Fronde of the 17th century, but what was it about centralized, absolute monarchy that drove "creativity"? How is it that states that appear nominally "more free" were less expressive artistically?
France was, and to some extent still is, considered a primary mover in areas of cuisine, fashion, poetry, intellectual thought, and general artistic expression, but compared to the Low Countries and England, individual expression was sharply and strongly curtailed. Was the patronage system intrinsically better than a free society for producing art and culture?
I submit that your premise is problematic. What makes you take as established that England and the Netherlands were less artistically expressive than France, either during the period you frame or now?
I'm not going to question your assumption that France was the center of culture because, in the opinion of most contemporaries of the time, it was. English royalty and aristocracy before the Renaissance both envied and copied much of France's culture, and were especially inspired by the court of Burgundy.
Now, to answer your question. In my opinion, you are correct that centralized, absolute monarchy was responsible for the excess of artistic culture in France, but perhaps not for the reasons you have assumed. Artists in France did not have that much more freedom of expression than those in England, as both would have been working for patrons who dictated their artistic subjects and styles. Therefore, neither artists in England nor France had any real sort of "freedom" of self expression in their works, even though the English were somewhat more politically free.
The explosion of refined culture in France was a direct result of the power of the French monarchy. The royalty and aristocracy of France were among the richest in the world--therefore, they had the leisure time and finances to commission the most refined and expensive art in Europe. Due to France's reputation of prestige in Europe, it was also able to attract the most talented artists of the time to their court.
I hope that answers your question a bit! If you'd like further sources or explanation, feel free to ask away. :)