That is a beautiful thing. So if I construct a block such that 100% of the clients fail on it, I can then have my own patched client control the entire BTC betwork, right?
No. You would have 100% control of the subtree following that failing block, but it would be very quickly outpaced by another subtree that the rest of the network would be working on. You need to construct a block that close to 50% of clients fail on, so that the network's work is split between two subtrees and they grow at about the same rate.
Well, if they crashed on a certain block then the operators of the client would notice and presumably update to a newer version of the client. The problem in this case was more subtle: the old clients did not crash on the block, they simply rejected it as invalid and continued working on an alternate subtree.
If you did somehow create a block that all clients except yours crashed on, you still wouldn't gain control of the network because the difficulty of creating a new block is calibrated according to the total power of the network, and only re-calibrates every few blocks. So for a while, you would still be effectively competing against the former power of the network, giving the client developers time to fix the crash.
