You're being too forgiving. TOS is not consistant with itself. At all. References dating the show vary from 200 to 900 years in our future, for starters. The design of the ship changes from shot to shot (when the pilot footage is reused). Yet as a fan you let it all slide.
I don't think it is that simple... as far as Science Fiction goes, TOS set the standard for consistency that most everything else since has been held up against. It raised the bar of what fans of SciFi were willing to accept.
That is the history, that is why (no matter what) Star Trek is above and beyond anything else in our culture.
But we can look at it more closely...
TOS was around for 5 years, had numerous writers and made 4171 minutes of episodes in that time. STXI was produced in 4 years by two writers and ended up with a 127 minute movie. Given that, I'm more than willing to cut TOS a lot of slack compared to STXI.
But above and beyond the numbers, the people who made STXI didn't consider consistency to be that important.
Were they wrong for not considering consistency important?
In 2010... apparently not.
But in 2054, who knows. I, personally, think they went for the short term box office gain over trying to make something with the staying power of TOS. I enjoyed it as a summer block buster, but it is already a last year movie for me (which is funny when you consider the fact that people who hated the movie care more about it than many people who liked it). And I sure wouldn't spend 40+ years focused on STXI the way that I have TOS.
And if anything, the biggest problem with the movie is that those who enjoyed it are generally apathetic to it. If they make another one, I really don't care. But that was the same problem by the end of the TNG movies too... I didn't really care if they made another one.
But by most standards STXI was successful. It sold almost as many tickets as TMP, it made more money than any Trek movie before it, and it won lots of awards. At the same time I have to wonder if it left people in the same place that Superman Returns did (a nice, enjoyable movie, both made about the same amount of money, but were generally forgotten a year later).
From what I've seen, a lot of people went to the movie (many more than once) and really enjoyed the experience... but we didn't really gain any new fans.
It would have been nice if STXI had as much depth of story as Avatar or Moon, but from what I understand the writers of STXI aren't known for that type of thing. But 10-25 years from now I doubt people will look on STXI as one of the important SciFi movies of 2009... it'll most likely be lumped in with Transformers 2.
But these were choices that the makers of STXI made, not mistakes. If STXI isn't as consistent as TOS, it wasn't a mistake... and needs no one to apologize for it.
Oh... and for the record, TOS Spock died in TWoK. So the fact that the doppelganger that assumed his identity doesn't have a clear memory of events which he didn't actually live through shouldn't come as a surprise to anyone.