Why do return envelopes in bills not have an address printed on them?

When I receive a bill in the mail (which happens with disconcerting regularity), I notice that they provide an envelope for me to send them a check but that this envelope never has the address of the payment-processing facility printed on it.

Instead, the envelope has a little "window" cut in it and I have to tear the payment coupon off of the bill and put it in the envelope just right so that the address printed on the payment coupon lines up with the window on the envelope. It's an extra step that doesn't seem to make any sense because they could just print the return address directly on the envelope rather than running the risk that I screw things up and put the payment coupon in facing the wrong way and rendering the mail undeliverable.

Nonetheless, it seems that everyone does this (or at least everyone who sends me a bill which seems to be most of the civilized world nowadays) so I suspect there must be a very good reason why they all do it this way. The only thoughts that I have are,

1. They're actually HOPING I screw it up so that the check doesn't get to them and they can slap me with a late fee.

2. They're not sure if they're going to be in business for very long so rather than order a ton of pre-printed envelopes, they order a ton of envelopes with windows in them so that if they go out of business, they can at least sell the envelopes with windows in them to someone else while the pre-printed envelopes will only be good for the recycling bin.

3. Somebody, somewhere made a law or a regulation that says they have to do it this way.

None of these seem to be a very satisfying answer so I turn to you, the gentle readers of Yahoo Answers, for your kind assistance!