i don't think it should be taken too seriously as an exact roadmap. I mean, if you look closely, you can see that the G4 is shown of having speeds of 1GHz +, whilst the G3 is supposed to be 'up to 450 MHz'. Seems more like a kind of mission statement, with relatively vague and flexible statements. So the fact that the G5 is intended to go from 800 MHz - 2 GHz shouldn't be taken as writen in stone, imo.
the motorola power PC roadmap for the g5 says nothing about altivec technology like it does under the g4 heading and in addition it says the next gen of g4 and g5 will be soi technology a technology that intel critizised ibm for coming up with yet now is trying to perfect on its own so it looks like the new chips will really be something seeing as it would beat intel to the punch!
oh and since it says nothing about altivec i wouldnt be surprised if big blue is helping develop the apollo and g5 seeing as they dont like altivec in the first place, maybe gigawire is the velocity engine's replacement?