Fermi was a significantly redesigned architecture on a new process (a flaky one at that) all on one step. That is why it was late. Presumably Kepler will be based on Fermi, just scaled up and tweaked. Nvidia's experience with Fermi and not very signifiant architectureal changes should mean a much more timely release.
Remember how late ATIs new architecture was (R600)? Then after that, how smooth everything went? As you can see, ATIs new Northern Islands architecture has been significantly delayed due to process roadmaps not hitting their targets, so instead we get Southern Islands which will be very similar to HD5000 and on the same process.
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