General Electric shares rallied sharply this week in the wake of a huge cash payoff from GE's sale of its remaining interest in NBC-Universal. One major reason was the expectation GE would use $10 billion to buyback and retire just under 5% of its total market capitalization. So did General Motors stock on the disclosure the auto giant was repurchasing 200 million shares of its stock from Uncle Sam for a cool $5.5 billion from the increased sale of cars.