It depends upon the nature of the plans. Plans that are very rigid and specify detailed product plans are bound to fail for the exact reasons that you mentioned. On the other hand, each division should have a direction laid out for them for the years to come. Part of the reason is that product development takes years (rather than months) Part of the reason is that technology doesn't move as quickly and unpredictably as you suggested over the short term. That is to say that companies should know what tablets and phones will look like in five years assuming that there isn't a major shift in the market.