Agreed, anybody who wants to have the latest and greatest for any significant period of time can not really buy a Tesla if the current policy persists. The likelihood of the product being superceded by the next version, or even versions, before you even get your car or very quickly afterwards is significantly higher than with any other car on the market.
That is something that one must factor in. I still wish Tesla would do a bit more pacing and grouping though. It might be wise. The AP1/P85D/85D was an example of successful grouping IMO. Had they done the same for AP2/P100D/100D (and maybe offered FUSC for that for a while), that would been a clearer buying opportunty for those who wish to buy/upgrade at clearly defined breakpoints. Doing it piecemeal (even more so when facelift etc. are factored in) makes things harder for the customers.
As it stands, Tesla doesn't really have any kind of such buying opportunities for that audience, which can lead to constant Osborning in the minds of some people. Why buy now when waiting a quarter will bring tangible benefits... and then the next quarter... and the next... Definitely those who already have a Tesla have been seen, at least somewhat, as decreasing their interest in upgrades. They can afford to wait - and this encourages them to wait.
Anecdotally, with the AP1/P85D/85D we saw tons more existing Tesla owners upgrading than now that people know every quarter brings major changes, sometimes even many times a quarter. (In 2012-2014 the changes that did come ever so often were, in the end, small aside from AP1/P85D/85D.)