A bank account is just like any other property. Whether or not your wife can access the full joint account will depend on whether you and your wife own the bank account as joint tenants or as tenants in common. Joint tenancy has the right of survivorship. This means that the property (amount in the bank account) is not divided into separate and distinct shares. When one joint owner dies, the other joint owner becomes 100% owner of the property. In effect, your rights/interests transfer to your wife. In this case, your wife will be able to access the joint account and use the account as if it were her own.
If, on the other hand, the property is held as tenants, then you each have a specific and distinct share in the property, which is usually 50-50. If you die, your share in the property will not go to your wife (as co-tenant) directly. Rather, it will go to your estate. If you have a will, this will be allocated according to your will through an executor. If you have no will, the court will determine who your estate is and the court (Supreme Court in your State or Territory) will declare an executor. If you have children, your shares will likely be distributed amongst your wife and children. If no children, then it will most likely be going to your wife, so no real difference in this case, except that extra steps need to be taken via the court.
You should contact your bank and ask in which state you and your wife hold the account. You may request to allow your wife access to the account upon your death. This needs to be organised with your bank.
Your bank should also have an FAQ section on their website that deal with the situation of deceased account holders.