I understand the frustration of the sometimes ambigous mutual representation of NW and KL respective business across the pond. Trust me that there are frustrations on both sides. I expect improvement in the coming years.
WBC on short European hops used to be amazing. Same great (old WBC) seats, full meals with cognac after, etc. even on 40 minute AMS-LHR. Thing is, if now your purchasing manager can put you on EasyJet for $50 he won't pay the $1500 for the WBC ticket anymore. That is why ES had to be introduced.
I wouldn't personally pay a nickel for Europe Select (which is explicity not called World Business Class since it is not) either. However, happily for KLM, the profits of AFKL and the long-term viability of the airline NW joint ventures with, many people and companies do pay substantially more for the extra flexibility and marginally extra comfort of an ES ticket. If ES were a just a space-hogging, FF program upgrade gimmick like NW FC, then NW WP members would also be upgraded on KL domestic flights. However, it is not. It is a money maker. No one goes into ES "just because" (unless they are an employee) without either paying or by being asked to help in an overbooked Y or W&B situation. Nevertheless, WP members share the same or even better priority for op-ups into ES as FB elites. And, if you are put into paid ES automatically from your WBC connection on your NW code-share, you can rest assured that there will be more newspapers & magazines, better food and better liquor then you will find on any NW FC US flight of equivalent length.
If it is any consolation, FB Platinum Elites are almost never op-upped on NW international WBC, only WP. And, the last time I spent more than $1.100 on tickets plus 25.000 FB miles plus $250 for a WBC upgrade AMS-MSP on NW metal for my family, the FA on aboard made a point of always serving them dead last, giving them no choice of meal and reminding them "they didn't pay for their seat"(!)
P.S. It is not true that USA residents cannot be members of AKFL Flying Blue. That was the case for KL Flying Dutchman, but is no longer so. If you are tired of earning double & triple miles from all the great WP promotions, want to deal with lots 0% and 25% earning fare classes on NW, KL & AF, like the idea of paying $300 in surcharges and taxes for a single "free" award ticket, etc. you might want to switch to FB!