All the endings were virtually identical except for the colors of the explosions on your screen: you died, the relays were destroyed, and the Normandy crashed. The end.
Whenever people refer to ME2's ending they refer to everything from the time you launch the suicide mission until the credits. Roughly 1 hour.
Mass Effect 3, people only refer to its ending as the final cutscene after you activate the Crucible. In ME2 terms this would be the little scene with Shepard walking past his crew, looking out into space, and seeing the Reapers descend on the Milky Way. Or the part after you choose to destroy the base or keep it could also be it.
Consider what Admiral Hackett stated. The Cerberus base is the first phase of the ending. The Earth phase is the second part. From Harbinger's beam to the Catalyst is the third part. Everything past firing the Crucible is the fourth part. The Extended Cut could be the fifth part.
If not, you can't possibly expect to have every single decision from ME1 to ME3 have huge consequences in such a short sequence. Consider the example above as "the ending", not the cutscene after you activate the Crucible. Taken as that, there is more than 16 differences.
For Mass Effect 2, getting to the base is the first part. The vent is the second part. The biotic escort is the third part. The part where you have to choose someone to escort the crew while you fight the human reaper is the fourth part. Fifth part is everything past destroying/saving the base until the credits.
And for the record, it wasn't just a different color. Earth could be saved (high EMS)/heavily damaged (mid EMS)/vaporized (low EMS). Normandy will crash, but it's engines break up (low EMS). No one survives the crash (low EMS), most do (mid EMS), everyone survives, engines are fine (high EMS).
Shepard lives (high destroy EMS), Shepard dies (everything else)
Full explanation
If you still don't think there's much difference, you need to think about it more.