Explanation/Reference:
"Each account has an account type. Account types determine how child accounts are aggregated to parent accounts and how account balances accumulate over time."
Above is an explanation about account types directly from the HFM Admin guide published by Oracle.
Additionally, this is true because Asset and Liability account types are balance sheet accounts and they represent a balance at a point in time. So, whether you look at the amount in these accout types as periodic, QTD or YTD, the value is the same as it is not a cumlative amount.
The Revenue and Expense account types are income statement accounts and therefore the QTD and YTD amounts are an accumulation of the Periodic amounts.