Some of those either come with caveats ('08 Cavs had one of the greatest players ever; ditto for '10 Thunder, although he wasn't quite playing at that level then), flat out weren't heavily favored (like the '11 Mavs, who many were predicting would be upset) or had a key injury ('12 Heat's only credible big played all of 15:48 in series and another of their big three played the first half of the series on a gimpy knee).
As far as the others, fair enough. But in none of those instances do I recall the vast majority actually thinking they were going to blow it and sure enough, they didn't. The Spurs have numerous times and not only would most not be surprised if they did so again, but many are now expecting it to happen. This is why this team is clearly not feared across the league and hasn't been for years despite their gaudy regular season record.
As far as your Spurs examples, they were not heavily favored in '03 against the Lakers and in '07 against the Suns, they were not only not favored, but they were considered the underdogs.