I admit, I am not reading impartial media. Most of what I see runs along the lines of "Let 7 Ride!" and "The AMA are stupid and should pull out of the FIM". However, I did do a little research and the whole "p-test" thing has been a peeve of mine since I joined the US Military 30 years ago, so I have amassed quite a bit of information. I am no expert, or a lawyer, but I am knowledgeable (and I stayed in a Holiday in Express once).
As Stu points out, when a sample is collected, it is tested only for key markers that indicate certain substances that they are looking for. They are only looking for these flags and others chemicals will not be in the report. Also (as Stu correctly points out) it is impossible to tell where the identified substance came from. Now if it was Cocaine, there is no (legal) way for it to get into your system. If it was Marijuana, some over the counter health supplements and even poppy seed bagels have been known to trip it up. For amphetamines, there are a number of legal uses but there are just as many illegal uses. It is a popular recreational and performance enhancing drug. And if you are a Rolling Stones fan, sing it with me: "She went running for the shelter of her Mother's little helper..."
:...What a drag it is getting old."
I think the thing condemning him is first, rather than deny it and request a second sample (which he can do), they quickly came out with an excuse. However, where that excuse fails is that in all these years, he never identified he was taking it AND he never failed a test before. Had they gave the (poor) excuse that his doctor changed the prescription and didn't inform them of the alternate substance (how many of YOU double check your doctors orders?), then I might have believed him and gave him a slap on the wrist. But when you have what appears to be a flagrant disregard for the rules...and with such high profile Doping cases (Lance Armstrong ring a bell?) in the international media, the FIM had to take a hard line stand - and rightly so.