I don't know about half, but you gotta think that once these guys began to realize that roids were the main target, they switched over to human growth hormone. BTW, testosterone is the most popular steroid and has been forever.
As far as chemicals and performance enhancing drugs go, the industry really hasn't advanced as much as you'd think. They aren't finding or inventing new chemicals that nobody else knows about. Conte refers to patches/gels/cream testosterones that have a half life of 8 hours, I've never heard of such a thing. There are different type of testosterones that you can take (3 main ones), that do differ in half lifes, but I've never heard the method in which they are absorbed make a difference in half life.
I do believe chemists can find new ways to mask the use of PED's though. Then again, testosterone is the most blatantly used PED in sports/bodybuilding. I don't know how they'd mask that.
I disagree with Conte, though, I think most guys are using growth hormone because it's so much harder to test. I don't think the MLB even tests for it, do they?