I wonder why he did it so abruptly right before a huge game like this. It seems strange that he would just up and retire out of the blue without giving advanced notice so we could have a farewell tour for him, especially since Georgia is in the midst of a national championship run.
I really hope that there isn't something seriously wrong with him and that this isn't an indication that things have taken a turn for the worst and he is about to die on us or something.
Perhaps he realized he was slipping and had lost a step (as several posters here have noted) and thought he couldn't do Georgia's upcoming historic season justice and wanted to pass the torch on to his successors while the season was young so they could use the championship run to solidify themselves in the hearts and minds of Dawgs fans as the voice of the Bulldogs (ie it will be his successors voices that people remember making the calls of this season that will be played back for decades to come, the new guys' analogue of Munson's Linday Scott call). Or maybe he just thought announcing a retirement a later time for his retirement would focus too much attention on him and he would become a distraction when the attention should be focussed on the boys on the field.
At any rate, I wish him well. He will be missed.