If Davis signs it, it'll be because nobody warned him about the implications of including pickup trucks in the new tax listing. Pickup trucks are used by small businesses, including many minority (Hispanic) businesses. The limousine liberals who live on the coastal plain don't drive such vehicles, but their contractors, plumbers, gardeners (and so on) DO drive them - every day. They have to drive them significant distances from the areas where they can afford to live.
If Davis vetoes it, he'll certainly point to the "working man" angle and shore up his support in the blue-collar community. I suspect that the bill will eventually return as a purchase tax on SUVs only.