You'll probably find that it is because this time you left the "Encrypt Wallet" option checked when setting the wallet password. If the wallet is encrypted, you need the password to decrypt it before the program can read it 
if it isn't encrypted, the main interface comes up straight away, but you obviously need the password to sign transactions etc (keys are always encrypted, regardless of whether or not the wallet file is)
If you goto: Wallet -> Password... put in a new password and uncheck the "Encrypt Wallet" and then restart, you'll find it won't come up with the "Install Wizard"
if it isn't encrypted, the main interface comes up straight away, but you obviously need the password to sign transactions etc (keys are always encrypted, regardless of whether or not the wallet file is)
If you goto: Wallet -> Password... put in a new password and uncheck the "Encrypt Wallet" and then restart, you'll find it won't come up with the "Install Wizard"