I broadly agree with the OP in so much that things like XP and "it just so happens these monsters were the perfect level" apply to D&D, and there tends to be some illusion that is constructed to help ignore them in play. I do not necessarily believe the same illusion exists in rpgs as a whole, and the D&D style level/XP/linear advancement model tends to be why in recent years I choose other rpgs as my primary games, but that's a conversation for a different thread. I only mention it because I wanted to point out that (I believe) the "illusion" is more of a D&D construct than it is something that is typical of rpgs as a whole.
For what it's worth, the 3.5 game I'm currently a player in does use XP, but the DM has said that gaining enough XP for a level doesn't automatically mean you level up. Instead, your character needs a week of downtime to complete the leveling up process when a new level is gained. So, say you're level 2 and gain enough XP for level 3, you now need to take a week of down time to get the benefits associated with gaining that level. If due to being busy or maybe you get lucky with a draw from the Deck of Many things, or whatever, you gain enough XP for multiple levels, you'd need multiple weeks to benefit from all of the newly gained levels.
For example, say that same level 2 character gained enough XP for level 3, but was busy fighting orcs and goblins, so couldn't level. The level 2 character finishes the campaign against the orcs and goblins with enough XP to be at level 4. It would take two weeks to completely level up.
The same DM also gives XP rewards for roleplay and various other things. He also requires many Prestige Classes to be qualified for in game. For example, if you were playing a Bard and wanted to become a Seeker of The Song, you would need to find another Seeker to teach you how to become one (as per the description of the PrC.) It's not assumed in his campaign that you can simply pick any option you want out of the book.
All things considered, I'm highly enjoying the game, and it's prompted me to look at 3rd in a new light. Some of the problems I've spoken of here on Enworld in different discussions still do exist simply because (I still believe) there are a few inherent flaws in the 3E design, but more than a fair share of the usual 3E problems have been (to varying extents) curbed by tightening the reigns a bit and making an effort to have in-game things matter more than the RAW built in metagame.
For what it's worth, not everyone in the current party is the same level either. I'm currently level 4 (nearing 5,) but a few of the other characters are level 6, and one of the other characters is level 3 (nearing 4.) I do see some problems with that due to how extreme the curve in 3E can occasionally be between certain levels, but, overall, it's going vastly better than I expected.