Understood. I'm not really trying to make you change your mind... just point out that you can- for relatively cheap. It's not just about picture quality, there's also sound (iTunes seems married to 1992's Dolby Digital at best while BD uses much more modern audio formats).
And I appreciate the concept of the conveniences of "buying" from iTunes. Of course, the issue there is that you don't own the movie- just a lifetime lease. You can't sell it, give it away, will it to anyone, easily loan it to a friend, etc. If you own the BD and make your copy from there, you actually own the movie or show and you have full control over the quality of both picture & sound.
There's also the scenario of deciding to just trust the iTunes storage in the cloud (not having a locally-stored version of the movie) and then losing the movie because the Studio pulled it from iTunes for some reason. This happens regularly- look it up.
Lastly, you make an assumption that Apple will offer an upgrade to H.265 for cheap or free but there's no obligation for them to do so. And certainly their Studio partners- who would actually make this decision- have a long history of wanting to resell the same stuff to us over and over at full price rather than upgrade the quality for cheap or free. I wouldn't bank on the cheap or free upgrade myself.
If you own the BD, you could make your own h.265 version and again pick your quality & sound levels. If there is an h.266, you could do it again there too. Each iteration would not come at a cheap (or not cheap) upgrade fee.
Again, I'm not trying to make you go one way or the other- just pointing out that it's pretty cheap to have much more control over what you want (with no dependencies on Apple or the Studios, no being at the mercy of potential future upgrade prices, no being locked into iTunes, etc). Chuck may not be the pinnacle of BD video viewing experience but someone who is archiving Chuck is probably going to archive at least a few great movies too. 4TB external is much cheaper than $200 right now.