jhine,
Luke 3:15 cannot possibly be totally inclusive of all people. Judea was only one small corner of the world even at the time and there were other civilizations that were simply too far away to know or care.
John 8:2 presents an identical problem. The temple complex could not have accommodated everyone in Jerusalem.
Similarly, if you accept the gospel accounts, it is clear that there were some who did not accept Jesus' message and others who actively opposed it. Luke's assertion that "all praised him" (δοξαζόμενος ὑπὸ πάντων) cannot possibly be totally inclusive. (Luke 4:15)
I only gave a few examples of this usage, but there are plenty of others.
Luke 11:41 is a different sort of qualification. Jesus did not wash his hands before dining like a good Pharisee should and responds to the surprise this causes by pointing out the superiority of charity over ritual cleanliness. Jesus' assertion that, "all [things] are clean to you" (πάντα καθαρὰ ὑμῖν ἐστιν) needs to be understood in that context; otherwise it makes no sense.