Fares with stopovers are usually cheaper than fares without - at least from destinations that are outside NL but relatively close - which is why they are now clamping down on short-checking of bags (for people who want to "jump out" at Amsterdam, they are increasingly attempting to hold baggage hostage - charging the €225 per bag retrieval fee (that was the amount last December, though subsequent posts here have implied that it's since gone up).

Just check KLM's prices from Antwerp, Brussels, or Düsseldorf and compare with the same destination starting from Amsterdam (though at least starting from Antwerp rather than Amsterdam will mean connecting from/to a train at Schiphol, so no baggage delivery issues there).