Any reason we can't skip our connecting flight?

You cannot do that. If you get off the plane in Amsterdam and don't get on the flight to Berlin, the airline will cancel the rest of your ticket including your return flight to the U.S. You can sometimes get away with skipping the final leg of your journey, but not an intermediate one.

It is a big deal because they don't what you might have checked through from the other flight. Maybe you left a present for the next leg.

Right, obviously that would be an issue, but as I mentioned in my question, we aren't planning on checking luggage. Obviously, that would be a bit of a problem :)

It doesn't matter whether you check luggage or not. Your contract with the airline is for a R/T from the US to Berlin. The fact that AMS is where you connect is largely irrelevant. If you get off in AMS, you violate that contract. The airline will know that you did not board the leg from AMS to BER because when you board they scan the boarding pass. The airline will view you as a no-show and they will then cancel all remaining legs. When you go to return home from Berlin, you will have a problem. The airline will either make you buy a new (more expensive) ticket or make you pay the change fee plus fare increase. If you want to see some real-life examples of this, get on the tripadvisor airline forum and you will see some real sob stories where people have done this.

I totally believed you, Laura! I checked it out and was surprised. We hadn't planned it like that, it just made sense when planning an itinerary. I didn't think it mattered since we'd already paid for the flight. It seems petty on the part of the airline. I bought a ticket, I expec it to be reserved, but it doesn't matter what I think apparently. It sounds like luggage would be the least of our concerns, even if we had planned on checking it. I'm glad I asked as I really didn't think it was a big deal. Thanks much for your response, it definitely prompted me to check it out further as soon as I saw your initial response!

We had our return flight cancelled from Melbourne to the US when the inbound flight was redirected. Weather conditions made it impossible to land in Sydney, so our plane was redirected to Melbourne. The airline collected our boarding passes for the Sydney to Melbourne connection when we deplaned in Melbourne and still cancelled our return to the US because we didn't board the Sydney to Melbourne flight - even though they never got us to Sydney in the first place. That was fun to work out.

In addition, while NO one on this board ever plans to check luggage.... It happens. Due to increasing luggage fees EVERYONE is trying the carryon route. Which means the overhead bins are FULL and people discover thier luggage gets checked no matter what they planned. So there are two things you should realize (1) always have anything of value either in a carry on that can under the seat in front of you are easily accessible to pull out and put under that seat when you have to give up your luggage and (2) it gets checked the final destination. There was a poster on Flyertalk a while back trying to figure out how to get his luggage under these conditions when he bought a ticket to city A and got off early.....(He had a one way ticket so the airline couldn't 'cancel' but they did send his luggage on to the "final destination"

Andrea... if you just want to stay in Amsterdam for a day or so you might be able to have that stop over on your flight. I have done that numerous times, it depends on if it is a hub city for the airline as to whether it costs more. You might check. I am assuming you were planning on finding another way to Berlin? You might also be able to change your flight to an open jaws if you want to simply fly to Amsterdam and fly out of Berline to US. Sometimes the change fee is worth it.
I have left the last leg of a flight in the past with my carry on luggage rather than take a 50 miles flight near my home, but the airline does not have to give you FF miles if you do that. I was lucky they did.

Thanks for your responses everyoneI am so glad I asked! I didn't think of it as a big deal. Good point about never meaning to check luggage, but sometimes it happens and I'll look into delaying the layover. Ultimately, we're not too interested in visiting Berlin, it was just the cheapest flight by a lotsaved us about $2,000 total for our four airfares so that's what we went with and now we get to see Germany too :) Just trying to avoid seeing Berlin twiceand I looked around for trying to get a flight into one place and out another but traveling in July, it was pretty cost-prohibitive. Thanks, everyone!