It doesn't seem to make much sense to me, since it sounds like they are still going to develop the platform for other markets. I thought one of the benefits of the platform was going to be that it would be designed for the start for use in the US as well as other markets to cut the development costs. So if they are going to develop it anyway, how much more could it really cost to develop a US platform.
S-man has a good point on what the competition has been up to also. However, its based in part on the competition's partners. Ford has done an amazing job at integrating its global platforms and taking advantage of its partners platforms and engineering strengths. The Mustang platform has roots in the Lincoln/Jaguar DEW platform. The 500 (fwd/awd) from the Volvo S60 platform. The new Ford Focus (not in the US) and Mazda3 on the Volvo S40 platform.
This is what Chrysler is up to also, using outgoing Mercedes platforms under new Chrysler models. (E-class under the 300, SLK under the Crossfire). Some initial reaction might be to criticize this move because those platforms are now a generation old, however I think its really a genious move. A prior generation Mercedes platform is probably going to be as good or better than any lower cost automaker's current platforms. So it allows Chrysler to put really high grade platforms under cheaper cars to make them much more competitive, and they don't lose their shirts financially because Mercedes already recovered a large share of the development costs. It also helps keep Mercedes an exclusive brand, since they are not sharing their new platforms with lower priced/branded cars.
GM on the other hand does not own any companies like Volvo, Jaguar, Mazda, or Mercedes with really good engines, platforms, etc to draw from. They do have Saab which benefits GM's 4 cylinder turbo engines, but that has not really helped GM much in North America so far. Their 20% of Subaru has netted them the Imprezza platform, but again, thats not been much of a help. How about a Pontiac built on the Legacy platform? I do not see where Suzuki or Daewoo add anything other than low budget vehicles to compete in developing countries and against Korean imports. They don't seem to be getting any real benefit from Opel or Holden either. My point, GM has not made the aqcuisitions (or been acquired) companies with some world class platforms and componentry like Ford and Chrysler have. Therefore, GM has to develop their platfoms themselves to keep up with the platform sharing going on at those other two companies. I don't know if its ultimately more costly or not, but it certainly isn't as easy or quick.
I think killing Zeta could be a huge mistake. Throwing all their efforts into trucks right now could be a huge error if gasoline prices continue to rise, and truck sales begin to decline. Not only will their resources all be tied up in vehicles that are losing popularity, they are pulling resources out of vehicle segments that are gaining popularity.
Can GM wait until beyond 2008 for some all new cars to show up on its lots?