You see, I expect the same would happen in any ongoing 3.x or Pathfinder game, too, especially when you get to what in 4e would be "paragon" tier.
That's certainly possible. I never had trouble figuring out that stuff, but I handle math pretty well compared to many people, and since we never ever used a digital CB in my 3e experience, we never had a chance to check it.
I can't speak to Pathfinder, as I haven't played it.
When it comes down to it, 4e's math is a lot lighter and more visible due to easier stacking rules.
This is probably true; I remember making epic level 3.5 bad guys and the math got really, really messy (attack values derived from base creature, advancement, class levels, size modifier, feats, ability bonuses... it's easy to miss stuff!). And God save me from trying to accurately figure out an advanced, epic-level wizard's skill points proper (tracking when his Int bonus was what, guessing on what magic items he had when, etc)... aargh.
Then again, it was totally satisfying looking at my completed (f'rexample) half-dragon shadow human wizard 16/archmage 3/custom prestige class 4, and the act of creating it was extraordinarily enjoyable... even if it took hours and the npc/monster in question might die before he ever got to act.

Likewise, making a high-level pc from scratch was fun but could take a ton of time if you wanted to research interesting options.
On the DM side, it's way easier - no modifiers for size or ability scores, simple formulas for attack/defense/damage ...
I am not arguing that 4e is super-simple or excessively easy to track. It's not. I'm saying it's not a meaningful distinction between 3e and 4e, so it puzzles me whenever it comes up. It's certainly not been in my experience - as I've said, I found HeroForge downright mandatory between skill points, feats, etc.
Again, agreed on the easier dming- that is probably my favorite aspect of 4e (and I love a lot of things about 4e- just ran my game last night!).
Like ... spells in 3.x? Or any of the more flavorful feats you'd expect out of any higher-level fighter type; a few from PF have been noted? Or class features? I can fit a high-Paragon Knight, Slayer, Scout, or Elementalist onto a single double-sided sheet pretty easily, complete with everything the player needs to know.
-O
Yeah, a lot like those things.

But see, you highlight one of the things about 4e at the end there- until the relatively simple Essentials class builds, it was pretty hard to manage a single sheet of paper character sheet that told you everything that you needed to know in order to make good choices in combat. Those builds have done an amazing job of alleviating that particular weakness, but until they came out there weren't many good options for a player who wants that single sheet of paper instead of a bunch of pages and/or cards.
Regardless, your point is a good one, and it's quite possible that the entire reason I never felt the same sense about 3e digital tools was that (other than the CD in the initial release of the PH) I never looked at any of them. Maybe all the characters in my 3e game had the same litter of errors as the 4e party; it's quite possible.