In later editions I think you notice it much more if the DM doesn't change things, is the difference; because of the more finely-tuned math.
Perhaps... but now that I'm able to see it (something I'll admit I couldn't back then), I don't see why I wouldn't equally see it playing an older edition.
That is to say, when I ran Caves of Chaos for the playtest I very much noticed the disparities between when we tested with 3 PCs vs when we tested with 6 PCs, and I noticed when they stumbled into 2 orcs and when they stumbled into 30.
The problem is still there, no matter the system - the expectation of coping is what's different. I'm not sure whether that's a good or bad thing.
Fwiw, I also noticed that one D&D Next PC was half as effective as another due to choices made, in the same way that I notice when playing 4e and we have some folks who are 3 levels lower than another, or have drastically worse treasure. It's not really something I noticed in my younger years when I played 1e and 2e, but I rather suspect I'd notice now.
I will say one thing that I think is a lot different. Much more so than in the past, people expect every encounter to be challenging. It's not enough that every encounter might cost some hit points, or spell slots, or have an extremely small chance to kill someone, but they want each combat to be meaningful and risky and require full attention.
And that's a _huge_ difference. In working on some recent adventures I positively confused people because I had a couple places where there were total pushover fights - mind you, it made more sense when they realized those fights were there to see if they sprung an alarm and were largely decided by initiative.
Hmm... maybe that's another thing. Initiative was _such_ a huge deal when dealing with spellcasters and dragons, but less so for goblins, ogres, etc. It feels like it's a pretty darn big deal for everyone now though. The easier it is to wrap up a combat in a round (sleep, dragon breath, fireball, very effective attacks of any sort), the more swingy it gets.