Miners have no incentive to employ monitoring of the blockchain via multiple clients like Eligius did to avoid mining any blocks on the invalid chain, if they're just going to be reimbursed anyway.
Except that in this case 0.8 miners were technically mining on a good chain and it was quite hard to detect that there was a problem. My pool has been always checking if it has the same blockchain as some other nodes, obviously this cannot cover all possible cases.
No, you mined an invalid block (under the standing Bitcoin rules) and other 0.8 miners were building on top of an invalid chain.
If you were testing against multiple implementations, you could have caught the problem as Eligius did.
(Not to say you are at fault for the hardfork, but these are the reality of it)
You are really crazy. Slush was creating blocks with "official" client and following the dev's advise to increase the block size. The block is accepted by every 0.8 nodes. What do you mean by "an invalid block under the standing Bitcoin rules"?
EDIT: If a bug could be considered a "rule", should we all move back to v0.1 as it represents the "orthodox" bitcoin rules?