I dont know if I agree with that, droid being 2nd and Eris being 1st, the droid came out BEFORE the Eris.
I would think the G1 is first gen, Droid and Eris would be 2nd and then there would be a grey area with all the 1ghz phones, they could be lumped into 2nd gen or they could be 3rd gen. Then would the 4G phones be there own gen or get grouped in with the the other 1ghz phones? The duel core would definitely be its own gen for sure.
The Eris was a glorified Hero. The Droid was a completely different beast. The reason I put them as separate was because the Droid had 2.0, and the Eris had 1.6 and last-gen hardware.
I actually wouldn't put the 4G phones as their own (especially Verizon's) because they're all based on older chipsets. They're still perfectly capable, but they're older.
Just to clarify my own little roadmap thing:
First-G1, Hero, Eris *any phone that was released with sub-2.x releases*
Second-Droid to Nexus one *the middle step from 1.x to the more advanced 2.1*
Third-Nexus one, Galaxy S, Desire, etc. *all the 1Ghz phones that exploded on the scene at the same time.
Fourth-Newer generation single cores, like MyTouch 4G, Thunderbolt, Revolution, Droid X, Droid 2, Cliq 2, etc.
Fifth-Dual cores
Like I said, I think there's a 4.5-gen category too, which the Charge falls into. The Nexus S could too.