I assume by "it" you mean "an attacker". It seems to me a bit clear now, but... just to make sure I understand it right. Based on my understanding of Satoshi's paper it follows that 51% attacker will be able to extend any block in the chain with probability 1 (provided the attacker has unlimited resources). Is this true?
And my second question: according to your first link:"...exclude and modify the ordering of transactions". What is the attacker's gain of changing the ordering of transactions?

Thanks!