I agree with Ashwin, but I can see how that phrase in the PMBOK could be somewhat confusing. It seems to imply that you are using software that has a direct electronic tie between the WBS and the accounting software. This is not necessarily the case!
The control accounts are merely the level of your WBS at which you choose to track costs and perform your EVM calculations. For sizable projects it would be prohibitively time consuming and expensive to try to track everything at the work package level (which is the bottom/most detailed level of your WBS).
Since the control accounts are where you are calculating EVM and other financials, of course they are "linked" to the accounting system. Just keep in mind that the link is not necessarily an automatic electronic transfer of data.