Conversion from AD&D to 3e was completely doable. It involved much more work than 1e to 2e, but things primarily worked the same enough to allow it. A 5th level wizard looked remarkably similar in 3e as he did in 2e, controlling for feats and magic items. They had access to the same spells, fireball worked pretty much the same, etc. That is not do-able with 4e due to the nature of the powers structure and the development over 30 levels.
The thing it, the individual elements may have "worked pretty much the same". The combination didn't. To use Fireball as an example, it still did the same damage, it was still third level, it still said the same things in the spell. And it was being targeted at creatures with more hit points and poorer saving throws, and instead of being a spell that would take off a high proportion of creatures hit points it became one that would take off a moderate proportion. Plus it was in competition with spells that when successful made difficult encounters into easy ones - the SoS/SoD variety - that when you note the deliberate way saving throws were made much harder in 3e than 2e were significantly more reliable. So yes, 3e uses the same names as AD&D much more than 4e does. But in play, it was D&D In Name Only.