Still more fun for me to watch a series like BSG than American Idol!
True, but squishing the timeline need not lead to the kind of contradictions we're talking about. There was no timeline-squishing reason to suddenly make 4 random characters (a drunkard and military disappointment? some PR flunky who happened to take Billy's position? a random mechanic? a former pro athlete?) "Cylons". It's not as if that was a development that was coming later and the fear of cancellation forced them to reveal it sooner. Instead it just came out of the blue and against all logic. You're right that cancellation threat had something to do with it, I think: namely, because they feared cancellation the writers figured they needed a ratings stunt. Well, they got one.
I also suspect there are changes of direction as the series plays out and the writers push off in directions even they did not originally anticipate.
Indeed, this is what happens and this is what writers do. But this is a problem for a sci-fi series like BSG because (1) 'consistency' is more important in sci-fi than in other fiction and (2) a huge part of the appeal of BSG, for the first 2 seasons at least, was that the story seemed well-thought-out and going somewhere. Both of these things have been tossed overboard. You're right that this probably happens to most TV series; if this were Melrose Place it wouldn't matter so much, but this is a science fiction series based on one giant story arc (humans attacked, flee, try to find earth). In that context such contradictions and ratings-driven 'changes of direction' are devastating if not unforgivable.