You've made these types of assertions before, and without proof. I'm not trying to be a Piper apologist, and if you don't want to listen to him that's fine by me. But you may want to consider that the problem may lie in your understanding, not in their teaching.
I'm willing to accept that, but I can point to several people on these forums confused by the same teachings of the same men. I know several people in person, as well. And people on these forums who are no longer here. But the quote I remember, if I could find it, I recall him directly saying that Christ died for all in a legal sense, but it is only efficacious for those who believe. How do you understand that?
Personally, I don't know what they believe, because I only find their doctrines a confused mess. But I also believe that people less analytical than myself, at least in certain regards of analysis (since I debate a lot), do not pay attention to the semantics of what they are saying, but the overall message. Rather, I think they may think they are preaching the gospel clearly, but I think their semantics are what is confused and it is allowing what they say to be interpreted incorrectly by it's hearers. However, I do find the same conclusion in several teachings in various materials produced by them, so I doubt it's just a mistake of semantics. So, I could also use the argument that perhaps many people have just become so accustom to accepting everything MacArthur and Piper say (as they are largely popular amongst some reformed crowds), that they've stopped hearing what they are saying. Thus the problem might not be in my understanding, but theirs.
Do I agree with some of there material? Yes. But I've found a lot of it nearly heretical. Namely some of their more recent books. And I can find you a dime a dozen who used to follow at least MacArthur 20 years ago, who don't anymore simply because of a few of his books that have a work-based salvific message in them. Again, I don't speak as someone who just reads his material. I speak as someone who grew up right next to his college, going to church with all his students, and everyone I knew basically idolized him. Of course, this isn't Piper, who I like more than MacArthur, but they teach about the same. Though I believe Piper is more genuine and not as arrogant. And though I should very much be addressed as carnal, as Paul did the Corinthians, and a young believer, I do believe they are teaching a false gospel that has lead MANY astray. I do not doubt some may have been saved through them, as sometimes confusion points of to the only Savior, as it did with me, but I also believe that those who take them as relatively infallible (and believe me, the majority of those people do -- and I do not doubt many hear feel the same certainty as their members, though they would not blatantly say it), have been lead astray (and I do not claim that this is an impossibility for myself either).
I've not provided "proof" because theological debates depend largely on ones interpretation. I'm not trying to prove or disprove anything Piper says, as I'm not trying to be right about anything. I'm solely stating that I've found contradictory things from Piper. If you want proof, just read thoroughly and extensively through his ministry, his books, his sermons. When you sit under those people for so long (as I did), you begin to notice that what they are saying does not add up. But maybe you can connect the dots for me when someone says that Christ died for all, but only died for the elect, and what that means.
I also tend not to provide extensive quotes, sources, etc. because I find it's waste of time as no one reads long posts or go to sites. In fact, I'd be rather surprised if 3 people read this entire post.