Not all that hard to figure out. Arnold simply wants to avoid pissing of the bulk of his base--the uber lefties and liberals. He's already lost the real conservatives along with plenty of the pretend-conservatives. The left, including the silk sock country club New Majority Big Tent elites, is all that remains.
Lots of the silk sockers that contribute to Arnie are among the largest contributors to the Preschool For All Proposition (Dick Riordan and his wife Nancy Daly; Reed Hastings; Warren Hellman; Rob Lowe and wife). You can also find David Geffen, Eli Broad, George Soros, etc.