Yes "war crimes" are decided by the victors. Yes there are war crimes that everyone agrees are war crimes such as the Holocaust, the Killing Fields of Cambodia, or even Shreverniza (sp?). But it was Curtis LeMay who stated it perfectly when her ordered the low level incidieray attacks on Japan by saying "if we were to lose this war we would be tried for war crimes".
But there have been Americans charged for war crimes. Look Mai Lai in 'Nam for example. We in the US don't call them "war crimes" per say because the culprits are charged as "regular" criminals (I am talking about things like 1st or 2nd Degree Murder or Manslaughter and such) under the Uniform Code of Law but they are still war criminals. I think the last American to be charged with war crimes was the CO of Andersonville prison during the Cvil War. But whether they are charged for 1st degree murder or war crimes, which are just titles, Americans have been charged and convicted.
Here is the thing about Ryan's books. You have to realize the time he was writing in. Unlike Ambrose, Martin, Liekie, Atkinson and so on, Ryan did not have access to the records that these modern authors had because of sometimes the records were still classified (for example it took decades for the bulk BIGOT documents to be de-classified) or inacceseble like some Whermacht records were in EAST Germany, not available to a American historian in the '50s or '60s. So when you compare The Longest Day to Ambrose's D-Day or Keegan's Six Armies in Normandy it seems incomplete in comparison. Also the books were written pretty close to the end of the war were there was still not much sympathy for the Nazis or the Germans in general. For its time The Longest Day, A Bridge Too Far, and The Last Battle were major achievements but because of new data or sources they seem a little dated. So don't knock the books just take them into context.
As far as the rapes the Red Army commited in thier drives west, they have become legendary AND THEY DID HAPPEN. Saying the wholsale rapes did not happen is like saying the Holocaust or the moon landing did not happen. I will have to agree to disagree with many of y'all for I have seen too many oral histories and read reports from human rights organizations about the amount of raping that went on. I will agree whole heartedly the Red Army was very brutal in thier conquests, I mean, liberation of Eastern Europe. And to say that many Red Army soldiers were tried and executed is laughable. Sure some were executed as examples but when its the commisar leading the rapes or Zhukov turning his back well things tend to get out of control. Many of you did not live through the Cold War so you never got see the tyranny of the Soviets and Communists (trust me Cuba, N. Korea, and China are mere pusscats now compared to how they used to be). And this is not propaganda, ITS HISTORICAL REALITY. Truth sucks. I accept the faults and failures of my nation and my ideology, do you?
Lastly about sympathy for the Nazis. I think, and you have to be a student of the US Civil War (read Confederates in the Attic by Tony Horwitz to study further my next point) and how its seen today in the US to understand my point. Here in the US the Confederates are seen under this light that they were fighting a "Lost Cause" and therefore because they were the underdogs they are are seen in a more romantic light. This the so-called Lost Cause Syndrome. Look at the movie Gettysburg and how "human" the Confederates looked and how machine like the Union characters were like as if part of cogs in machine. Look at movies like Stalingrad or The Battle of Britain, or Cross of Iron. They are made to look more "human" than thier Allied or Soviet counterparts. They always seem to have this espre de corps or panache that thier enemies lack. Look how many people reenact Whermacht or SS units in the US. (and yes in my neck of the woods we even have a Red Army and Soviet partizan reenactor units too). I am not saying that Nazism was good (HELL NOOOOOOOOOOO!!!!) but we also sometimes forget that the German soldiers were human too and had the same fears in combat that thier Allied and Soviet counterparts had in combat. They too had mothers.
So if many of y'all disagree with me, its is your right in a democratic society, but I have history on my side, for good or worse as its reality is.