Financial and Insurance questions for PcM

While studying the financial and insurance areas for  the PcM exam, I wondered about the following...feel free to include your explanations as, I am sure, other people here may wonder the same.

Financial Questions:

1.  Why isn't Indirect Labor considered as Overhead?

2.  Is a Chart of Accounts the same as a ledger for double entry bookkeeping?

3.  Is Total Overhead the same as Indirect Expenses?  (sort of the same as #1)

Insurance Question:

1.  Why can project specific insurance be billed to the client as a reimbursable expense?  How often is this really done?

Thanks all for reading.  Hopefully someone has some explanations.