No-one is criticising continuous-improvement itself - just the lack of transparency and predictability. As we're seeing: people are saying that had they known a significant upgrade was in the pipeline (which will undoubtedly affect the future resale value of their cars, let alone the quality of the user-experience) they would have postponed their orders.
The advantage of "model-year" updates is that they generally happen once per year - while this does result in a slowdown of sales near the end of the predictable product cycle it gives automakers and sellers an opportunity to sell at a discount, and customers are fine with that: they're saving money knowing that they're not going to be getting the very latest. But with how Tesla's doing it right now it's a crapshoot that can lead to pretty bad buyer's remorse.
So we want continuous improvement - by all means, but I think we should get some kind of advance-notice if a significant upgrade is forthcoming (say, 3-6 months forewarning). We're already committed to buying the car so Tesla won't be losing money - and plenty of people might not care for that particular upgrade (e.g. I don't care for the vanity-mirror upgrade or new interior options, but I do care about the computer).
I think there needs to be strong consumer-protection laws. Tesla's cars command high-prices partly because of their high resale value - but that's predicated on the assumption the cars will be usable in the long-term future. The only way to guarantee that is to require manufacturers to make their parts available to third-parties on a reasonable and non-discriminatory basis - just like patent law. Corporate greed should not harm society (for example, increased junking of otherwise perfectly fine cars that just need one or two parts that the owner couldn't source).