Secret Question - answered in 3-5 mins, how.

A general question in how the iSignThis service works. I'm familiar with Paypal in that I have waited for a number of days in order to check my bank account solely in order to answer Paypal's question, how many cents did we deposit into your account.

In the first instance I understand how this works; I submitted my bank account details and so Paypal merely transferred money into the account. I'm assuming there is no direct relationship between Paypal and my bank (or any bank for that matter). For this particular process, Paypal is at the bank's mercy, in that it takes the bank 2-3 days to record the deposit in my account.

From what I can glean the iSignThis process is more or less the same; the only difference being is the time taken to answer the secret question is about 5-10 minutes. I'm assuming that as an end-user, a purchaser of something, I will have to open up another browser window, login to my bank account, retrieve the secret amount, return to the merchant site and input the secret amount; and presto, I'm verified.

Why is it that in iSignThis's process, their deposit is immediately recorded and yet, Paypal's is not?