(prepares to be shot down)
When you travel by train or bus/coach on a non-local journey, you take luggage with you for your trip; the same "assumption" has been applied by the airlines over the years. I suspect that a vast majority air of passengers will take luggage with them and therefore expect, that just like the other modes of transport, when they pay their fare it includes a luggage allowance.
What seems to be happening is that rather than an "all-inclusive" fare as major airlines used to charge, the young upstarts are now implementing a "compartmentalisation" approach (probably a marketing guy's idea) whereby a low headline-grabbing price is advertised but by the time you add in the cost of buying the ticket, adding some luggage, pay-to-print boarding passes etc etc, the fare soon costs more than that of a reputable, established carrier. Possibly this is along the lines of, in the UK the "delivery charge" that was for many years a non-optional "extra" when buying a new car.
IMHO an advertised flight price should include all the "essentials" that a majority of passengers expect (ie includes a reasonable luggage allowance, printing of boarding passes, payment fees etc)