Its not the $$$ that bugs me, its more that convenience. I know that I often put off dealing with bills because I don't have stamps and I don't have a chance to go buy any. Usually I'll let several bills pile up so that the trip to the post office doesn't feel so pointless. If each bill came with a SASE, I would probably write checks for them as soon as I got them.
I would even be ok if their bills came with a little +$0.34 to cover the postage for that month. Like I said, its not the $$$, its the convenience. Then again, I suspect that people who bill you (esp credit card companies) know that little things like that matter, and its in their best interest to do little things that might make your payments late by a day or two, just long enough so they can hit you with the late charges and raise your interest if they want to.
Every once in a while capitalism is disillusioning... and then I get to bill someone multiple k$ for some trivial (to me at least) computer job and its all ok again ;).