"May be higher" is a gross understatement. Is "provably much higher" is closer to the truth.

There are a few classes of users. If you're the type who always uses the "I forgot my password" workflow on sites then you probably are the type who will lose your keys.

But if you're the type of trader who makes a trade and then forgets about it for a while you're at risk of losing the funds left on the exchange - like with Paypal.