How on earth can it be that many of the things that Jesus expected did not happen?? This just doesn't make sense to me. So, if 'this generation' ONLY entailed the generation living in Jesus' time, this means that we HAVE to conclude that Jesus was wrong, and that some of the things he expected didn't happen. Since it seems totally unlikey that Jesus could have been wrong, don't we have to conclude then that there should indeed be a greater future fulfillment?
But you are assuming that what the anonymous author of Matthew says is synonymous with what Jesus originally said. How do we know that the author (or the authors of the other gospels) isn't putting his own words into Jesus' mouth? Why is it that Matthew has reworded the disciples' question in 24:3 (compare with Mark 13:4 and Luke 21:7)? Indeed, the original phrasing of the question in Mark and preserved also in Luke implies that the coming of the Son of Man and the destruction of the Temple (see Mark 13:1-2, Luke 21:5-6, Matthew 24:1-2) were connected -- for in his reply Jesus mentions the "coming of the Son of Man in great glory" and celestial signs as part of what would happen when the Temple is destroyed (Mark 13:24-27 in reference to 13:1-3). But the parousia did not happen in the wake of the events of AD 70. The question is modified in Matthew 24:3 so that the disciples were asking him about several different things, including the parousia and "end of the world" in addition to the destruction of the Temple, which were implicitly tied together though named separately. Since Matthew was written after Mark (as indicated by the fact that most of the text of Mark was absorbed into Matthew), it makes intuitive sense that Jesus would not be the one who lumps together the two but that his disciples would do this (as it was the Christian community, Jesus' disciples, who had expected the end then) so that Jesus could clarify the matter in his reply. The author still clearly expected the end to come before the generation that rejected Jesus had passed away. So, in essence, AD 70 had failed as the date of the second coming, but the parousia was still very soon. This fits very well with a date around AD 80-90 for Matthew, as many scholars have suggested.
http://www.jehovahs-witness.com/10/83341/1364935/post.ashx#1364935