I think this is much ado about nothing in this case. While searching by price only, nwa.com shows you the base fare in large bold text; the total fare including all taxes and fees is shown about 1 inch to the right of it for all to see. If you search by price & schedule, nwa.com just shows you the total price with taxes & fees as you select each segment, it doesn't show you the base fare at all until the end. DL's search is fairly similar to NW in showing both base fare and total price.

This is FAR more transparent than the mechanism that AA, WN, and CO use on their websites. AA and WN let you pick each segment from the matrix by the base fare only before adding the taxes & fees. CO shows you a round-trip base fare only until you've actually selected the flights and moved on to make the purchase.

FL is even more convoluted, quoting you the base fare + departure tax in its matrix, then adding in the remainder of the taxes & fees when you move on to purchase. Likewise, YX includes some tax in the fares shown on its initial selections, but then adds the remainder of taxes & fees after selecting flights.

As I recall, AS shows you only the base fare in its fare matrix, but has a pop-out on the side that adds together the fares you've selected and the accompanying taxes & fees to keep a running total. NK shows you base fare in the matrix, then shows you the total price for that segment below once you select which base fare you want.

G4 basically gives you no information on total price until you've entered all of the passenger information. Their fare calendars show you the base fare only for each day, then below indicate the range of total price that may be charged based on every day shown in that month on the calendar, so it doesn't give you much indication of YOUR actual cost unless you are selecting the cheapest or most expensive segments.

For what it's worth, amongst the "big" American carriers, I believe only F9 and UA actually give you only the total price when searching for flights. In both cases, you finish the selection process for your desired flights before they break apart the quoted price and show you how much of that is base fare and how much is taxes & fees.