Peter:
This is an excellent re-observation on your part and IMO an even better point of view by the architect, even if it wasn't said by me
To me this thinking is most relevant in modern times with technology and length fighting the preservation of design integrity and the spirit of the game. We have all beat to death the issue from the tee and those architects who don't worry to much about this aspect give appropriate attention to the short game, where overall, this seems to be the greatest opportunity as an equilizer and the element of great fun and creative interest.
Sure, with the great sites these conditions of fun and interest and even challenge can be met from tee to green. All the better are the architects who don't have a great natural site, but are able to bring it all together from start to finish. On a whole, however IMO, shot-making and the short game have proven to be the most vulnerable elements in a players handbook, and the best area for architects to draw inspiration from the past masters for defense, to instill thinking, to 'level' the field and to ensure great fun. Don't get me wrong, I don't mean to suggest that we disregard play from tee to approach/green, but the thought and challenge of recovery is not only the management directly associated with getting up and down, but it is IMO and should be directly proportional to the decisions made at the tee and in the LZ...it is just unfortunate that more golfers don't learn this until they are 55 years old
"I have to admit that I've never looked for or noticed or paid attention to this aspect of golf course design; and when I think about courses I like, this criteria has never been on my radar screen let alone something I've used to judge a course. And honestly, even now that I'm thinking about it, I can't imagine being able to notice this 'variation of difficulty'."
Peter, you may not have 'noticed' this aspect, at least not intenionally, but if you play enough different courses or see enough, you can begin to feel it and 'see' it when you become familiar with what you are looking for. Some designers are more deliberate with their work, or in bringing out these conditions and others allow or make it happen without much notice. I happen to like the latter moreso, because it lets the consequences unfold through the discovery/experience process, rather than as an immediate response as so many like to have occur. This goes back to why so many great courses do not show their many faces until repeat play. So much depends on any given day and moment depending on where your ball ends up.
This 'variation of difficulty' I believe rings true in the best work of the present and of the past. It does favor a great site at least in the ability to make it happen more naturally and randomly such that it is more refreshing to experience, but through the works of many architects we talk a lot about on this site, I believe they take great care and pains to get it right and ensure these characteristics you speak of are in place to create the situations you speak of. So obviously, I really appreciate these 'features' and conditions, for without them the game would simply not measure up, or keep me coming back, or inspire me as a designer.
Thanks Peter for bringing this up