There's no way you can equate carbohydrate/protein drinks to steroids/EPO/HGH. The side effect of too carbohydrate? You might get fat.
Steroids/EPO/HGH side effects? Testicular shrinkage/cancer, hip necrosis, heart attacks, agromegaly, immune system compromise etc etc. A number of pro cyclists died in their sleep in the early 90s because their blood hematocrit was over 60%. Great for aerobic capacity, not so good for regular heart beat when sleeping.
So let's leave the arguement "it's all performance enhancing" aside. They are not the same. There are real risks with using these drugs, and cyclists shouldn't have to be forced to use them to make it in the pros. That's what USADA is trying to do.
As to why people are dropping the dime on Armstrong. First off, I suspect they feel some guilt for their past sins of doping. You combine that with the fact that the Feds came around and told them to fess up, or spend a lot of $ defending themselves against sanctions which would effect their ability to earn a living with the short amount of time they have left in the sport. So they made their lives easier and rolled over on him.
I rather doubt they rolled because they thought he'd be a good patsy. It's clear that the guy likes to fight, and make life difficult for people who cross him (Simeoni, Bassons). They did it because it was in their best interest to do so, and they can feel good about knowing it might help clean up the sport. Equally, I doubt they made shit up about Armstrong. That's a great way to get yourself in serious hot water.