Odds are people will attempt to port everything to weaker devices as well.
lets face it.. the weaker devices are all a lot of people are going to be able to afford. For example motorola backflip is free from radioshack online atm.
My girlfriend ended up getting the backflip for that reason. She worked out a deal with her parents for the 30$ a month data package..
However, they would have *never* considered shelling out 500$ for a nexus one.. they just can't afford it.
Also for what its worth.. I HATE that people are pointing this out about android.. Has no one ever looked back at iphone and said "well with all these different versions coming out, how long until I can't get updates because I'm on an older version?"
Lets face it.. with every piece of non upgradeable hardware we face that problem. Even the nexus one has a 1ghz snapdragon processor according to moore's law will be obsolete in two years.
Now sure some of you out there say "well yeah but, two years if the average life of a phone" which is true.. but, what about all the people who buy a nexus one a year after it comes out? thats 500$ gone if they had just waited a year.. But, a year is a sizeable part of life too..