A few salient points:
1) As has been pointed out numerous times (and ignored by many in the Kool-Aid crowd) the 3G was sold right up until June of this year. That means it is a current phone, not a two year old obsolete phone.
2) Do I think Apple deliberately tried to brick the 3G, no of course not. I had one and when I upgraded to iOS4 it became very slow and unpleasant to use.
3) Is Apple obligated to provide new OS's for older devices (or indeed any devices), of course...