I don't entirely agree with this. In the dice analogy it would be more accurate to say that once a "1" is rolled the person who rolled the "1" will no longer roll another "1" because "1" has been proven to not be the solution to the problem at hand. That is, he would reduce the number of faces on the dice before rolling again. I agree that each attempt has equal chance of being the right solution in that the chance of rolling a "1" was just as good as rolling a "6" and that on the successive roll the chance of rolling a "5" will be just as good as rolling a "6" but chance of rolling another "1" has now been made zero and the available pool of possible answers has been reduced. Since the pool of possible answers is finite and thus every attempt proven incorrect will not be reattemtped the next attempt does run a statistically higher chance of being the correct answer than the previous attempt.
This is exactly what I mean by wasted work when a block solution is found by someone else. This analogy seems better to me. Anytime you have to chance something besides the nonce in your block, you're starting over.
Sure, but that has as good of a chance of helping you (by preventing you from wasting time on a block that wasn't solvable) as it does of hurting you (by keeping you from getting to the later solution that might have been in that block). In the end it's a wash.