I have been a Flight Dispatcher for KLM and I can tell you that they have a very healthy and safe fuel philosophy.
They monitor their fleet 24/7 and they have realtime info about the amount of fuel they aircraft are carrying. Flight Dispatch does pro-active checks of weather and traffic situation at destination and they give crews advice about this in case of interruptions (or possible expected interruptions) of trafficflow at destination.
Yes, crews are asked to think about the amount of fuel they want to carry, but they are totally not unsafe. It has happened maybe a few times an extra landing was planned for extra fuel-uplift, but this was because they had more headwind/lower Flightlevel than expected and has only happened a few times in the last 10 years of active dispatching. They did this to stay on the safe side of the legal limits and out of trouble!! So in my opinion you can't compare this with actual flying into your Emergency Fuel at all!!!
And crews easily take 20 mins extra fuel if weather deteriorates. And in case of expected delays/diversions the crews will get an alternate that makes sense. So not all to Rotterdam, but for instance Brussels/Antwerp when coming from the south, or Dusseldorf when coming from the east.
If weather is really much worse than expected and the longhaul flight are already arborne, then the flowcontroller (monitoring slots) and Operations (monitoring overall flow of fleet) gives other airplanes (short haul) some delay, cancellations or rerouting via a different IAF to prevent holdings/delays to other flights. I know about a situation that we gave an airborne flight the advise to divert to Düsseldorf, but the Captain had taken extra fuel and was willing to hold at Amsterdam. But in that case he would have caused extra delays to other (more important) aircraft. So we explained the situation and he diverted to Düsseldorf and flew to Amsterdam after weather improved and trafficflow permitted his flight.
I've been preparing flights to Madrid, and those flightplans always needed extra attention due to trafficflow at Madrid. They standard got extra fuel based on statistical info and we planned the longer routing (arrival via the south and landing in northerly direction). And inflight we monitored trafficflow to advise on possible delays. And Captains could easily take extra fuel without any explanation
May I also inform you that KLM Dispatch is using CFMU...! After login on the CFMU (Eurocontrol website) you can exactly see all traffic and slots (airborne and 'planned' traffic with EAT). So we could determine how many aircraft would land within a certain time period at a destination. This means flights are given advise to increase/decrease their speed to stay out of these moments of increased trafficflow and to limit any holding delays or unwanted fuelburn.
In my opinion traffic management (and fuel decisions) are very well integrated in a safe environment at KLM. And in my opinion very few airlines are so wel prepared and monitoring their fleet. Yes, it may have happened that an aircraft had to divert, but this was only to stay out of trouble and to cause as little as disruption overall to its fleet!