Why does blockchain.info report "Estimated Confirmation time" not as 10 minutes? Currently, it is a timer which counts down from 10 minutes starting when the transaction is first seen. When the timer reaches 0 minutes, it switches to "Unknown / Never." 

It is my understanding that finding blocks (and confirming transactions) is a Poisson process, hence the correct value should be a constant "10 minutes" and then "Confirmed!"

Is my understanding wrong?
You're correct; the expected confirmation time from any given point in time is always around 10 minutes (it may be a little more or less when the network hash rate has changed since the last difficulty adjustment). This question looked at that exact issue.

Note that a retailer (or other transaction acceptor) doesn't necessarily need to wait for a block to be solved in order to accept a payment though. More info here:


How has the problem of waiting for confirmations been eradicated?
How do I safely accept bitcoins without waiting for confirmations?