Not logical
There is no reason all the additional forces being sent to the Gulf now could not have been sent earlier when we were building up the original forces. In fact, given the need to get the war over with before summer as you point out, it would have made far more sense to have all our forces in place to assure a more swift victory. Unless of course Bush and Co. thought the additional forces weren't needed, which was EXACTLY what they thought. Bottom line, Bush miscalculated. Both he and Rumsfeld rejected the overwhelming force doctrine -- UNTIL NOW. Let's hope it doesn't cost too many lives.