Remathilis
Legend
1. The game offers more stuff at levelup than in 1E/2E so people look forward to it.
Yes. Pre-2000 D&D had fewer decision points as the game progressed (class and race being fairly static choices made at char-gen). So while a magic-user may look forward to 3rd level spells or a paladin to his warhorse, most classes got their toys early, making build unimportant. Feats, multi-classing, power-suites, prestige classes, and especially "traps" (intentional bad choices, such as 3.0 toughness) made build important.
2. The time to level up has decreased so the next level is always a few more XP around.
Yes. the 10-13 encounters to a level has made them feel more anticipated.
3. Todays gamers are expecting more instant gratification. I blame video games for that one.
NO!
"Those darn kids" didn't ruin D&D for you, gramps. There were always players who built monstrosities (munchkin wasn't invented in 2000) and who cared only for XP-grinding. 100th level PCs existed in days of yore. Similarly, some games (early Final Fantasy, for example) where leveling didn't give you myiads of choices when you level; they felt much like D&D levels: some more hp and maybe a new spell.
The recent trend among all media has been for "total customization" so its no suprise D&D, like CRPGs, MMOs and other RPG games, opted for games where you can tweak your heart out. It makes sense; it gives players a more tethered feeling of ownership and allows the company to sell new "options" (splat books, DLC, whatever).
Watch before you generalize