Well, the facts that cars are getting heavier is rather a common trend that happens everywhere. I mean, even modern porsches weight a lot these days...
Sadly enough, but I guess that's one more incentive to remove the backseat etc... 
Well, add A/C, airbags, power-steering, lots of computers and so on to an old porsche and see what happens... It's all that comfort/safety stuff that makes a car fat!
But fortunatly because of better tires, suspensions, engines modern cars are usually as fast as old ones.
On the other hand... I saw a comparison of old and new hot-hatches on tv, cornering ability, acceleration and stuff. The old ones won clearly!
