So this is about how some choices didn't properly carry over into sequels? Specifically DA:O into DA2.
It isn't feasible to carry over every choice and some stuff just has to be retconned.
Yes. But there are some things of note:
The confusion stemmed from relatively small choices that could easily be carried over. Specifically the death of characters that, previously, didn't have some worldwide importance to the plot. The writers chose to give certain characters, namely Leliana, more of a spotlight afterwards, which they certainly didn't have to. But, as it happens, the writers liked that character so much that they couldn't create another one to fill her completely new role, as if synapses are a rare commodity.
Wether one favours C&C within a single game doesn't matter. Cross-game C&C wasn't just advertised but whenever the writers decide to change the continuity they retroactively devalue the player's agency in those old plots. You may not care for this (and I wouldn't blame you for it), but it would be like saying that Skyrim could have shipped without dragons because you don't particularly like them. We are discussing a failure from the developers and there's no spinning it.
Finally, while all you said is true, it doesn't appear that BioWare would dare and say it. But they totally could. A lot of people retcon gargantuan continuities because they simply can't keep track of it. Blizzard does this all the time. But, of course, BioWare's reputation as MASTER STORYTELLERS® wouldn't allow them to.
What's worse is that in keeping that reputation BioWare doesn't just follow a possibly unattainable goal, they (through Gaider) are also absolute assholes about it. I wouldn't mind if he just came out and said 'oh, we had this really cool idea and couldn't pass it on'. I'd just say 'well, just be careful with the continuity, else people will just stop caring about the story altogether' and move on.
This advice comes from experience. I used to keep track of the Warcraft setting's lore but, unfortunately, Blizzard's reins on their writer's whimsy just isn't as tight as those over their art departments. They just can't let go of dead characters so, of course, death is an empty plot point (notice the parallel). A new writer steps in, adds their own special buttefly of ideas, completely changing the tone of central characters and voilá, I just don't care anymore. Nothing is surprising because everything is surprising - there's no continuity because its effectively retroactive.
Of course, Gaider sounds like a very bitter man. So its just natural that he can't be humble about his choices. The setting is his and he can do whatever he wants.
What's funny is that this probably is a lot of noise for nothing. After all, they've commited to keeping the big choices intact (specifically the Old God baby). Smaller 'inconsistencies' are, in Gaider's own words, perfectly explainable. I don't know if it was already, but one rather obvious possibility is that Leliana is potentially undead. That wouldn't mean there's nothing to learn here - keep the suspense, but try to make it obvious that past choices had an impact. Make it obvious that there was no retcon. For one, you could have made Leliana's identity ambiguous until the time of the big reveal (and 'I WAS POSESSED BY THE MAKER' or whatever). But why learn when fans can be blamed for their silly, heretical, headcanons?